An incredibly illuminating time with Adam at METL, who has an interest in damascus/wootz blades and has visited Al Pendray's shop in Gainesville.

Boy was I/most of us confused

1. This is rivelling from plastic deformation during the rupture - NOT the crolle pattern. I think Will & Craig called this one



2. Adam, on initial examination, did NOT identify low cycle fatigue but suspects an area of embrittlement at the forward, lower point of the blow out. He agrees the deformation superiorly looks like there was a bulge.



3. Unfortunately, composition testing by EPX, SEM, or OES will require a piece of a Damascus demonstration rod at least 1" X 1" and with the layers of steel and iron at least 1/16". The dense matrix of iron and steel will not allow analysis of each component separately. SO if someone would please whack off the end of their demonstration rod, we could do the testing, then try to match each with the modern equivalent



4. Photomicrographs of the barrel wall should give us a definitive diagnosis, AND identify interlaminar rust, voids, inclusions, micro-fractures, defects. Adam does NOT think the fracture lines follow weld lines.

5. Adam does not believe MPI/Magnaflux testing would be the best procedure to identify defects in the barrel walls by NDT. Gloria a Dios there is another testing lab in Phoenix that specializes in radiographic (x-ray) testing of metal and I will set up a meeting with their engineer.
I'll have two barrels for radiography; one of which could then be sectioned to identify any defects found on the x-ray testing and possibly blown up to see if the blow out occurs at the defect.

Adam shares my excitement about doing something no one has done before, and I am hopeful that the x-ray testing (of course combined with wall thickness, chamber, and bore evaluation) may be a way, and at less cost, to establish a GREATER (but not definitive) level of confidence in the safety of Damascus barrels.

Again, many thanks to all who have contributed opinions and suggestions!!

Thanks Drew.

I hope that part about embrittlement is not the case, as this would pertain to all old guns Damascus or fluid steel.

ninepointer brought this up earlier.
"Something I've never seen discussed at length is, notwithstanding adequate wall thickness etc., can metal fatigue be an overlooked factor in old doubles? Metal fatigue is usually not detectable to the naked eye or through caliper measurements. Yet military research (albeit that research has been mostly done on very, very big guns) has clearly established that metal fatigue in such guns is real and that the safe and useful life of a gun has its limits, even if that gun was always operated within its design specs. Formulas have been developed to predict when a military gun needs to be taken out of service."

How does the overpressure that was indicated by the extractor imprint on the steel base of the hull figure into this explanation?

I need to know how embrittlement and plastic deformation would not be mutually exclusive.

My working hypothesis, and feel free to post yours:

1. An unknown (and likely never known) something obstructed the bore
2. Pressure rose proximal to that obstruction.
3. The rise in pressure caused a bulge, which caused the rivelling.
4. The rise in pressure caused the expansion of the base of the hull's steel head, and the extractor left an imprint on the head (both described by Burrard)
5. When the capacity of the chamber/barrel proximal to the obstruction to contain the pressure was exceeded, the barrel blew (in at least 2 pieces but NOT along ribband weld lines), possibly starting at the area of embrittlement.

IF METAL FATIGUE IS PRESENT, microphotographs will show evidence thereof. Adam described it as the appearance of the sand at the edge of the shoreline ie. layers of wavy lines.

Although highly unlikely the obstruction may well have resulted from "shot bridgeing" where for some reason the shot was fused togeather and did not compress when it passed through the forcing cone perhaps caused by hot gas escaping around an ill fitting wad.

Good stuff Doc Drew. Was there any comment about the appearance of the grain of the steel. I'd guess that the same steel with a finer grain would be tougher and more resistant to failure. Any comment about possible preexisting defects, maybe the bright metal of the sudden failure is different from the occasional small pockets of dark appearing maybe oxidized pits that may have been there from before the mishap.

Any thoughts as to why the barrel appears as though pressure vented in a limited area and doesn't appear to show 360* signs on the inside of the barrel. I'm only being curious, and thank you for looking at it a whole lot closer than these things tend to be.

I agree with all 5 points, except the part about brittle.

The metal shows ample evidence of elasticity in the bulged part.

I eagerly await more information Drew. I'm not a metalurgist I'm a drunkard, which at least according to Captain Renault makes me a citizen of the world.

SGJ: I edited the original post for clarity. Again, initial visual examination did NOT suggest low cycle fatigue.

"IF METAL FATIGUE IS PRESENT, microphotographs will show evidence thereof."

Ah!

So there's no presumption of a fatigue condition.

Maybe it was the 'low cycle' thing that wasn't in my lexicon.

One would naturally think 'high cycle' might be the appropriate term, but specialists tend to use cryptic terms.

I'll edit my post so I don't look like I completely lack reading comprehension.

Drew,

Thank you for the great effort. This certainly is an interesting thread, in addition to the related others.

Your ...

"IF METAL FATIGUE IS PRESENT, microphotographs will show evidence thereof. Adam described it as the appearance of the sand at the edge of the shoreline ie. layers of wavy lines."

... was what I was referring to when I used the term "beach marks" early on.

When reading that the gun had sat around wet for a couple days I pretty much crumbled-up that paper (the thought of possible metal fatique from repeated firings of max loads) but I am still looking forward to seeing the microphotographs.

Thanks again,

Mark

Drew,

This opportunity for testing is awesome! I'm glad that Adam told you that composition testing would require a larger sample. That is what I fully expected and why I was suspicious of the metallurgical testing company that told me they could provide results from patterned damascus. I feel good about who you are working with.

It's very hard to do an accurate visual examination of the barrel metal through the photos. But, I keep looking at the grain structure of the steel along the broken edges. It appears to be of very large grain size. Large grain size in steel looks like sugar crystals. Small grain has a dull, gray appearance. If the grain is large, this would suggest that the steel was not thermal cycled enough and/or properly to reduce the grain size after forge welding. Large grain would not be terribly surprising. As I discussed in another thread, the barrel smiths knew that cold hammering improved the steel, but did not fully understand that it was the repeated heating and air cooling (thermal cycling) of the steel that caused a reduction in the grain size. The degree that the barrels were cold hammered, varied by the quality of the barrels. Too, the smith's skill at heating the barrels properly for grain reduction was surely a factor.

Large grain in the steel will weaken the steel slightly, but should not be considered a major defect or weakness. Though if embrittlement occurs, it would most likely begin in an area of large grain size, vs. small grain.

Photomicrograph examination will be very interesting. I think you may be amazed at how clean the steel is. I suspect that only a few very small slag inclusions will be found.

If composition testing of some demonstration rod material becomes a possibility, I might be bold enough to post up a prediction of what will be found. I'm fairly confident in what I believe to be the major alloys in the two materials. I haven't had time to do the research that I hope will help to determine the trace alloys. Let me know if you get some samples to test and I'll try to get my research done. I may end up looking like a fool, but I think it would be fun to see if my research is accurate.

I would expect, in the case of an obstruction, that the barrel would have blown just prior to that obstruction. I still lean towards an overloaded cartridge theory. I still think it may be worthwhile sending the photographs by e-mail to the Birmingham Proof House and seeing what their theory is. I'm sure they will have either seen it before or created it with their lab experiments. There's 200 years of experience there at the click of a mouse. At the very least they should be able to narrow down the search field. Lagopus.....

I still cling to the belief there was an obstruction. The exact location of a burst in relation to said obstruction is also related on how much the obstruction moved upon being hit. If it was solid & unmovable then the burst would have been behind it. In the case of a movable obstruction the burst may actually come forward of where the obstruction initially was, the amount dependant upon the resistance of the obstruction. Another thing to consider also is that at this point in the barrel the inner wall is supported by the other barrel, the point to where they become separated has not been reached. Consequently I do not see it as unusual the bulge was confined to the outer wall.

I have nothing constructive to say, but what you do is amazing. Wanna save both threads, along with whatever's forthcoming, and study it carefully. My compliments!

I seems to be possible. I think I can see machining, honing?, marks just opposite the bulge, they appear crisp and unaffected by the pressure it might have taken to the blowout in the other direction. It seems like in the chamber maybe about mid hull the scratch pattern is smooth and it seems like the measurements say the chamber may be bulged back by the case head.

I wonder if the pressure spike was actually in the chamber and too high, or built at too quick a rate, for the metal to deform. Maybe at the bulge the pressure was dropping to allow the metal to act in a plastic way. I think the picture of the monosteel blowout in part 2 on Feb. the 5th. shows similar, but may also be more of a 360* bulge.

Thanks again Doc Drew for digging deeper. Maybe back to the reloads you took apart, you could tell something about the depth of crimp or possible primer substitution. Could be a moving obstruction from a load that pressure spiked and the old Remington just had enough of. I've wonder if Tony T's barrel crack right out of proof would have looked similar if someone had put a few more rounds through it.

Craig, in your last paragraph about the depth of the crimp or possible primer substitution, Joe Wood loaded that exact recipe but doubled the powder and if you look at his post with the picture you will see it did not or could not crimp.
Also unless it was a magnum primer such as a Federal 209M or CCI 209M the increase would not be substantial.

I posted on Shotgun World on the Reloading Forum and received many response about dropping a double charge in Mec Progressive machine.
Some said yes, but one poster said this "Powder does not fill the bar of a MEC until the bar goes fully left, it drops the powder when it travels toward the right.".
If there was a powder bridge in the tube, the shot would not have fallen in the previous load, or everything would have fallen.

With most of these newer components, there is minimal wad pressure, mostly less than 20 lbs. If there was a double charge of powder and IF the shell crimped the wad legs would be crushed and you would have to use close to 100 lbs. wad pressure, but you would see that before hand.

Drew,

I will be very interested to find out what you see via x-ray.

I had x-ray and magna-flux work done on a handful of barrel sets 20-25 yrs ago. My own experience was that neither process was definitive. A couple of tubes had pitting and I would have thought that something besides just the puts would have shown on those, but no. Advances have been made in x-ray technology, and hopefully you will gain more insight today.

Postscript to the above - they were all Damascus barrels.

Drew,
I've sent the links to Peter Powell at the Birmingham Proof House.

So you picked up on the 'Casablanca' reference, but I bet you had to look up metal-lurgist.

There a Tom Armbrust article I believe on his website floating around on the net that shows about 1500psi swings just on primer swap (different powder on that test). Also, he showed a target load using Clays powder that rose about 1800psi only on depth of crimp changes. There were some folks that thought the original load was on the warm side for the gun, and I was thinking small variances might have been feeding the gun higher pressures than it seemed.

Craig, yes I have also read Tom's reviews and I will agree there is much to know in reloading. I have also seen a powder that just substituting a primer only changed it a few hundred psi.

There is a lot of information on reloading on Shotgunworld in the Reloading section, many have had loads tested and have shared their results. Most all will agree that shooting in the 8,000 psi range, a primer substitution will not bring you close to SAMMI's pressure for 12 gauge which I believe is 11,500 psi.

I do have to agree, that his load was high for a vintage gun no matter if a Damascus or fluid steel barrel.

Damn I missed that. Love that sort of thing.

I don't know what may have caused it, but it looks like a severe over stress of one or few cycles.

The large crystal structure is what I'd expect for Damascus given how its made. I would think a low cycle fatigue failure would show striations.

If you can perform some hoop tensile tests of samples from the barrel just ahead of the failed section, I think it would be very telling. My wild guess is that there was no metal deficiency that caused or significantly contributed to this.

I made a fixture to do this testing a number of years ago and sent it to a member in Oregon.

Who would venture a guess on the pressure this failed at?

Been following these threads with some interest and have to say this is some of the best forensic detective work I've seen in a long, long time. Y'all are to be congratulated and encouraged for it.

Now for my $0.02. I believe the consensus has coalesced around there having been an obstruction in the barrel. I recall part of the early discussion being that there was snow in the area when the gun was dropped after the blowout. Could the obstruction, which seems to have been the cause, have been snow itself?

Getting a clot of snow in the barrels is something I'm always watching out for while hunting in winter conditions. It has happened to me - thankfully I caught it before firing - and I can say it does happen without even noticing it.

Not really- I may not be one, but I know how to spell that word- the AWS Welding Journal and also the Lincoln Electric Co. "Stabilizer" use that word in reference to a welder's need to know the basics of both ferrous and non-ferrous metals identification- ie: spark testing on ferrous metals, etc. There is an old but true saying that a good quality weld depends on 90% proper preparation, and basic knowledge of metallurgy is part and parcel of that. And with that, you can "Knock on wood"- with or without Mr. Dooley Wilson on the "shortened Steinway"!!

Very well. You do know the movie.

Chuck, given the case head expansion into the extractor groove, I'd guess someplace north of 40K PSI.

That's a steel head on those shells, and they are noticeably harder to resize than brass heads.

My SWAG is well in excess of 15K psi. Say 25,000 psi.

1) I base this on my estimation of the strength of the Damascus being around 60,000 psi ultimate, providing for mild steel being around 64,000 psi, and ductile iron being around 60,000 psi and some conservatism.

2) I used .100 as the Min Wall

3) A hoop calculation of a .798 I.D. chamber and .100 wall with a 60,000 psi strength is around 15,000 psi.

However, you can see the chamber wall is much thicker at the rear. Of course, my math could be all wrong too.

I've seen lots of barrels bulged or even blown because of snow obstruction - quite a common occurence over here - and I don't believe this is the case.

The snow-caused damage invariably happens either before the choke, or mid-barrel where the barrel walls are the thinnest.

As a matter of fact, not all snow obstruction does damage to barrels (that's why it's so common - people get to be careless). The light, christmass-card-flakes sort of snow hardly ever does any harm. It takes heavy, wet snow to get the job done.

In order to blow the barrels in the chamber area, it would have to take a whole lot of wet snow somehow working its way to the chamber area and freezing in place there.

i have seen barrels damaged from snow- the damage was at the muzzles, i would expect that to be the norm for that

I asked METL to proceed with a formal failure analysis, and here's the estimate

Per your request the following quotation is for testing of the component submitted to determine the root cause of failure. Testing is to include preparation, analysis, examinations, photographs, and report.

Misc. sectioning and preparation of the sample: $40.00
Photomacro/micrographs (15 estimated at $15.00 each): $225.00
Metallographic mount and preparation (2 estimated): $105.00
SEM/EDX examination of fracture surfaces: $175.00
Metallographic Examination – Including metallographic examination, failure analysis, and full written report documenting all findings: $630.00

And some other stuff. Could buy a decent 16g shooter instead

The good news is that 3 articles will probably come out of all this, with the remote possibility that someone might pay me for the information:
A Blow-Up Post-Mortem
Damascus Mythology and Reality
Non-Destructive Testing of Damascus Barrels
Not sure what would be the best forum; possibly American Rifleman?

The next part of all this is to explore with Team Industrial Services here in Phoenix either MPI or (Adam's advice) radiography to identify wall defects. I will have:
The blown out 2 Iron Remington barrels
2 Iron Smith barrels
Chain Smith barrels
Damascus-Twist Ithaca barrels
and possibly a JABC Twist barrel.
The Ithaca barrels are unusable, so if a defect is seen, METL could then section the barrel and identify exactly the nature of the defect. I would also expect the different patterns to be apparent on x-ray?

I don't believe TEAM is a charitable organization either, but it's all in the name of science
and so far my long-suffering spouse is buying it.

as for a venue - I doubt you would find a more interested audience than either DGJ or Shooting Sportsman

To be clear the information above is not a solicitation for donations to the barrel testing cause. Please see my post in Misfires.

For the service that seems to be presented, the cost looks to be very reasonable. Maybe a nondestructive testing recommendation at a fraction of the cost could come of it. You may, but I don't think, you'd see much of the damascus pattern on an xray. If the alloy components that cause the different colors are able to be distinguished by xray, I think the image would be muddied because it likely lays at random diagonals through a section of barrel. As you noticed though, most of the defects do not seem to follow the damascus patterns.

MORE PROGRESS for Part 3 of this quest

I'll be meeting with the NDT manager at Team Industrial Services and will take a barrel donated by a fella here which is a candidate for destructive testing related to over-honing. Decided to do BOTH MPI (first) then radiography to compare the sensitivity for identifying wall defects (hope there is one!)
The cost is $125 for each test. If a defect is found, THEN METL can section the barrel and identify the nature of the defect.

TEAM has international offices and is throughout the U.S.
http://www.teamindustrialservices.com/

IF radiography (which is certainly interpreter dependent) turns out to be both sensitive (if it's there, it's there ie. no false negatives) and specific (if it's not there, it's not there ie. no false positives) that might be a helpful NDT for $125.

and



Good to know this - your answers exclude one possible source of the obstruction problem here.

Change of plans. Decided to take another barrel donated by a fella here, with the previously posted bulges



Might be very interesting to compare radiography of normal barrel with the bulge section. AND have another Chain Damascus with a bulge on the way
I do expect (eventually) to have a barrel with a defect identified by MPI or radiography that can then be sectioned for analysis and microphotographs.

We routinely employ radiography at work and it is quite expensive. How much money have you sunk into this project so far?
If you do come up with a way to test intact Damascus barrels and reliably determine their integrity and safety, that would be a landmark contribution.

Virginian: I'll tell you in about 5 hours Meeting TEAM this am.
Please see http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=357346#Post357346

Another VERY informative meeting with the lab manager and two of the NDT techs at TEAM. They also agree that radiography will be a better test to identify defects within the barrel wall, and can do elliptical views to isolate the wall (amazing!)
We are going to start with MPI, then will x-ray any abnormalities seen by MPI, then x-ray normal barrel, then x-ray the bulge, and generate images for publication of everything.

One of the techs was so excited that he headed back to the lab to start even before I was out the door

I believe we are going to end up with a cascade of complementary evaluation options based on one’s toleration of uncertainty, and bank account :
1. External visual inspection
2. Internal visual inspection augmented by direct or digital images the length of the bore
3. Chamber length, forcing cone length, and bore measurements for evidence of alteration from the original
4. Wall thickness measurements from breech to muzzle
5. Non-destructive Testing (NDT); likely radiography
6. Proof testing to at least 1 1/2 times the psi of the shooter’s intended load

Anything else?

Drew,

I don't ever recall seeing a basic strength of materials analysis of damascus - e.g., things like tensile strength, toughness, break load.

While this would be a sample of one, it would be really interesting to see how the properties of damascus compare to common homogenius barrel steels.

This analysis would be different from the analysis of the barrel failure that oriignally prompted this inquiry, but I think would be interesting nonetheless. It sounds like you are working with the guys who could provide this pretty quickly assuming you could give them samples of the right dimensions.

Good luck,

Ken

Thank you Ken. A tech at METL was breaking bolts when I visited. The one barrel that I have which is a candidate for destructive testing is pitted and over-honed Damascus-Twist, but the chamber might be a candidate for testing.
I did find these references to Whitworth, Krupp, and Seimens steel, but need someone smarter to tell me what it all means, and how they compare to 4140.

http://books.google.com/books?id=ycUOAAAAYAAJ&pg=PA614&lpg

http://books.google.com/books?id=czsyAQA...p;q&f=false

Drew, thanks again for your great work and research.

I'm sure there are enough people here, and I am included, that would help donate money to this great cause. If it is ok with Dave to do this, then you cant set up where the money could be sent.

While all barrels including Damascus would be of a different analysis, it should be close enough using what you have being tested.

Here you go David, and thanks
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=357346#Post357346

Possibly the Xray findings may validate the use of one of the surface dye tests, or some simple screening to decide if a more extensive look is needed for a set of barrels. Thanks for the updates Doc Drew.

Interesting old thread here regarding steel strength

http://www.doublegunshop.com/forums/ubbt...&PHPSESSID=

Steel Type Max (lbs/sq in)
Damascus ------- 31,291 to 52,626
Typical 1905 Steel -- 64,000
Winchester Steel ---- 39,400
Winchester Nickel --- 88,600
Krupp Special ------- 85,340
Krupp 5 M ----------- 92,450
Bohler Antinit ------ 116,630

Great thread, the education has been so helpful!!

OH BOY! TEAM has already finished the MPI and radiography on the Smith No. 0 barrels with the bulge, and I'll be meeting with the metallurgist Weds. am.

AND I'll take this barrel for radiography of the bulge and normal barrel. Smith 4E Chain Damascus with a left barrel bulge from .735" at 3 1/2" to .758 at 4 1/2" with a minimum wall thickness at the bulge of .077 compared to .090 on the right. There is also a segment from 12" to 6 1/2" from the muzzle with a MWT of .016 on the left.



The barrels are unusable, but as 4E barrels, it would not be unreasonable to fit full length 20g tubes to the barrels.

Burst or no burst, bulges seem to have an affinity for predictable areas. Hope they have interesting findings for you, and maybe trends start to emerge.

Several images. Obviously these have been resized but I have viewed the original digital images and they have excellent definition and resolution. Clearly TEAM is on uncharted territory as they also have found no published images of radiography on pattern welded barrels. They are of the opinion that MUCH more information can be obtained from radiography compared to MPI. The ONLY finding on MPI was an 'indicator' at the sauter.
Just like an MRI of a lumbar spine, the results require expert and experience interpretation, by human eyes and we will need LOTS more barrels (ie lots more $s ) to clearly establish what the images are showing, and possibly sectioning and photomicrographs to confirm (more $s)
One major issue is if the less dense areas within the barrel wall represent voids, slag, inclusions, etc. or it they are from the pits. The techs are going to correlate the images with visual exam using a bore scope and we should have the answer.
One myth we can slay now is 'the wall is nothing but a mass of welds, defects, inclusions'. The wall looks like solid metal; like any pipe.
So here goes gentlemen

Negative images highlighting the probably pits





Positive digital images

Likely tool marks when the chamber was extended. The linear marks are unlikely to be from low cycle fatigue, but that may require photomicrographs



Large arrow is solder at rib extension and barrel junction. Second arrow is the bulge and you can appreciate less wall thickness ie. less dense. Lower arrow is porosity in rib solder



Probably pits rather than voids, slag, impurities in the wall

Just guessing, but I'd think slag from welding or inclusions in the original material might show as circumferential elongated forms as that's the direction that the steel was drawn while being forge and welded.

If those roundish spots are pitting, I'd think they'd be easy to see. Maybe if the barrels look smooth, they could end up being possible hidden defects. Might be tough to tell though exactly where those spots are, and the bulge picture doesn't seem to have any of those funny looking spots around it.

Here is another to add to the mix --

http://parkerguns.org/forums/showthread.php?t=12809

I hate to add a discordant note to Drew's excellent work and his current working thesis as to the cause but Burrard describes the obstruction bulge as being caused by the momentum of the forward rushing gasses being stopped suddenly by the obstruction. That is, the momentum of the gases at the rear of the barrel causes the gases to carry forward into a high pressure zone at the obstruction and further raise the pressure and then the ring bulge results. Had the barrel wall been so thick and the obstruction so solid that no burst had occured and the gasses allowed to quit rushing about and then the pressure of the contained gasses measured that pressure would be much lower than the pressure required to deform the barrels and make the bulge. If it were not for the momentum of the gases near that are crashing into the obstruction that pressure would not go so high as to cause a bulge. Since the bulge occurred right at the forcing cones I don' think there was enough velocity for the gas momentum to cause a high temporary pressure large enough to burst the chamber. I think it was just an overcharge or an overcharge and a defect in the barrel.

I have become confused which barrel we are talking about on these various threads. I am talking about the damascus barrel that recently gave way on Drew's friend at the skeet field.

Thank you Dave; I totally missed that. Just so we keep the infro together in one spot, here are the images, and my response








By the appearance of the blow out, I think there is little doubt that there was an obstruction, likely at the forcing cone, and would suggest that you examine every empty used prior to the event for a missing base wad or piece of plastic. AND please check the shell that was in the chamber for expansion of the head, and an indentation on the head from the extractor. Because of the plastic deformation of the chamber, I am quite confident that this was not simply a fracture of the barrel wall.

A formal failure analysis costs more than $1000, but if you would like to send me the remains, I could measure the wall thickness around the blow out and also ask the Metallurgical Engineer at METL for his opinion. Possibly a visual exam of the edges would confirm my thoughts.
Also please send the remnants of the shell, or post an image of the head.
Another option would be destructive testing of the remains, with sectioning and photomicrographs. This is the big $s.

Wait wait wait!

Drew... these pix aren't of the Remington barrel that started all this.

This is a CHAMBER blow out.... a clear result of an over load.

that is the gun Researcher posted the link to the Parkerguns forum about

Why is it that all the blown up guns I have seen have involved reloads but we keep looking at the gun for the problem?

+1 Exactly my thoughts. Until they quit reaming, honing, re-choking, and loading shells with C-4, this will be a never ending phantom chase.

In Weak Rivets, a Possible Key To Titanic's Doom Speaking of slag.

Progress report

Was back down at TEAM this am. They had a bunch of images of fluoroscopy of the first barrel wall to confirm the defects were indeed pits and not within the wall. No image yet but I'll post the best when received.
Still working on the second (Chain) barrel and bulge.

I'll have 3 more barrels to x-ray so we should generate a meaningful data base of what normal pattern welded barrel x-rays look like, and hopefully will identify a definite abnormality that can then be sectioned and photomicrographed. AND a fella on the PGCA site has had radiography done on a set of barrels with a fracture and will try to get digital images from the folks that did the testing for me.

No word yet from METL regarding the Failure Analysis.

I'd have thought pattern welding would show manufacturing defects here and there, but the xrays seem to show the appearance of a mono steel and they seem to fail like a mono steel. Maybe, the forging process to make damascus barrels was intended to minimize the effects of any individual material defect like inclusions or process defect like slag.

"the x-rays seem to show the appearance of a mono steel and they seem to fail like a mono steel"

By Jove, I thinks he's got it And I hope we'll prove it with the photomicrographs of the blow out barrel, Whodathunkit?!?


BTW: in a remarkable event of (Providential?) timing a fella named Chris Helms sent a bunch of pics from a rib relay which demonstrate just what we are seeing on the x-ray
http://www.picturetrail.com/sfx/album/view/24519472

if you have ever forge welded iron- when it is hot enough to work, it flows together

Maybe the old timers really knew what they were doing... :-)

Very much appreciate the donation of a 16g Syracuse Arms Co. Twist barrel which sadly was likely the victim of an attempt to lengthen the forcing cones, and 16g short magnums



Both chambers still 2 9/16" but the MWT at the end of the right chamber is only .087; left was .110.
Note the No. 0 16g Smith had a MWT at 3" of .114 right and .120 left.
At 3 1/8" there are four 1/4"-3/8" bulges; at 2:00, 5:00, 8:00, and 10:00. The WT at 3" was .098 and I was able to get the pin in the 5:00 bulge and the WT was .093. On the surface, that bulge appears to have a crack



At 5 9/16" there also appears to be a surface crack. WT there was .050



So the barrels are unusable, except with sub-gauge tubes BUT will be perfect candidates for radiography to confirm the depth of the cracks and possibly section and photomicrograph the cracks and the bulges. Knowledge advances

Still waiting to hear from TEAM about the Smith No. 4 barrels. METL should have the failure analysis done this week.

Will be dropping off the above barrel with TEAM Monday am, and hope to have more images to post. Still no word from METL

And mailed this request today. I've not found any documentation as to who/why the shell makers decided to place the warning. There was a reference to SAAMI here

August 24, 1948
Remington Arms Company Inc., Service Division
Subject: Heavy Loads in Damascus Steel Barrels
A number of accidents have happened in which Damascus barrels have been blown up with progressive smokeless powder. It has been felt that the reason for this was not only that the loads were heavy and that the guns were not designed for such loads, but also that there is a possibility that such barrels have become weakened with the passage of time due to unsuspected corrosion to which they are susceptible to a much greater degree than modern types of barrels.
It is a great many years since Damascus barrels have been made and sold by American gunmakers. It is felt that unsuspected corrosion of this type of barrel is making the continued use of these guns a hazard.
The conclusion was reached some time ago by the Technical Committee of the Sporting Arms & Ammunition Manufacturers’ Institute that sportsman should be warned against the use of present day smokeless powder loads in such guns regardless of whether they are heavy loads or so-called light loads.
H.L. Hendrix


Rick Patterson
Managing Director
Sporting Arms & Ammunition Manufacturers Institute
11 Mile Hill Rd
Newtown, CT 06470-2359

Sir: I am researching an article on Damascus shotgun barrel safety. Could you please confirm that the "These shells must not be used in guns with Damascus or Twist Steel barrels" warning on shell boxes appeared in the late 1930s as a result of a recommendation by the Technical Committee of SAAMI? Would you have a copy of that recommendation? Does SAAMI now have a position on the use of Damascus barrel shotguns with smokeless powder loads?

Gee... wonder what they might say....

Hoping not to waste Mr Patterson's time, I did check the site
http://www.saami.org/
The shell box warning does not appear, nor could I find any mention of Damascus outside the glossary.

I doubt if there will be a response, to a non-member, but if forthcoming will let the curious know. If someone here has a connection with the Technical Committee, I would most appreciate you making inquiries.

+2

Interesting to note that when a steel barreled gun blows up, which happens about as often as damascus guns, ammo is usually the first suspected culprit.

There have been a number of guns "Blown Up" having steel barrels & firing factory shells. They just don't attain the Notoriety of those having Damascus barrels or using reloaded shells, or Both.

Yep. I know of such a case and his settlement with whomever prevents his discussing the incident.

Exactly - well put.

It may not be all bad to note that the reloads in this case were looked at a bunch more carefully than we normally get here about. Still, there might have been loads available that weren't so high a pressure under ideal conditions for typical clays shooting.

Almost any time something looks like a bulge in a barrel, there seems to be a lot of feeling that an obstruction was present. There's probably different situations. I think we're lucky to get a little different look at the barrels through the efforts here.

I wonder if this is like saying, "Most tire blow-outs on Trans-Ams involve mag rims, so mag rims must be the culprit."?
Never mind the fact that most Trans-Ams wear mag rims.

Similarly, because of the special dietary needs of vintage guns, I'd guess that a high percentage of such guns are fed reloads. So yes, when a vintage gun blows there is a good chance the shell in it was a reload. But is there a relationship?

UPDATE:

1. No word from SAAMI

2. TEAM has finished radiography on 3 barrels but final analysis awaits the return of the senior tech from Hawaii. I hope to find a crack on the Syracuse Arms twist barrels, which can then be sectioned and examined by METL

3. Fascinating meeting this am with Adam at METL. We reviewed most of the images, both SEM and photomicrographs 20X to 100X. He's going to send a very interesting image which I'll post soon, and the other metallurgists in the office are having a grand time looking at something never before recorded (the exciting life of engineers! )
Very short version
a. There was no evidence of low cycle fatigue
b. The blow out was from an over-pressure event with ductile (stretching and sheer) fracture, with nothing to suggest an intrinsic wall defect. Photomicrographs can not prove obstruction vs. shell overload, but certainly the bulge suggests obstruction.
c. The failure did not occur at a ribband weld line
d. One crack in the piece that was retrieved was just that; a fracture through a cast iron section. Another crack did follow the low carbon/'mild' steel - cast iron juncture in one of the rods ie. within the scroll.
e. As above, the images show mild steel - cast iron - and interfaces with some blending of the metals.
f. Adam showed me a freshly cut piece of the barrel fragment, and it looks like any other cut of metal ie no 'orange lace'.
Monty sent me a pitiful Smith Twist barrel with marked rusting in the bore. I'm going to use it for tensile strength testing, but first will have Adam examine the cut edge for evidence of the mythologic interlaminar rust.

Tensile strength testing update:
I've received contributions of 3 Twist, a Damascus-Twist, and a Crescent Armory steel barrel to section and destroy. A Parker Vulcan steel is on the way. I'd very much like to have 2-3 higher grade Crolle barrels and more fluid steel pieces.


For comparison, I thought I'd include Zircon's examination of 2 Sherman Bell blow-up barrels. Remember the barrels were subjected to sequentially higher and higher pressures.

http://www.familyfriendsfirearms.com/forum/archive/index.php/t-55364.html
The damascus barrel let go by a mechanism known as low cycle fatigue. Each succeeding round had higher and higher pressure. After several rounds, a crack started to emanate from the extractor screw hole. Each successive round caused the crack to open up just a bit further, until finally the overpressure could not be contained and the remaining ligaments failed in a ductile fashion. Ductile failures in steel look like a taffy pull at about 1500 to 3000X magnification using scanning electron microscopy. There is a cup and cone appearance with a lot of microvoids present. This appearance is a dead-set giveaway to a ductile fracture.

The homogeneous, "fluid steel" barrel failed by brittle rupture. The fracture surface is more or less smooth, but has some "rivulets" in it that point back towards the initiation point, which was the screw hole, again. The fracture surface was about 3X as long as for the damascus barrels. In other words, the same 30,000 psi final internal load created a lot more fracture surface in the homogenous barrel than in the damascus barrel. This indicates that, for an equivalent-length fracture, it took less energy to open up the homogeneous barrel than for the damascus barrel.

In the case of the damascus barrels the crack spiraled around with the weld pattern, but it was not on a weld, rather it was on one of the in-between areas. The spiral welds remained tight and the parent metal is what failed. This may seem pretty amazing, but in many, many instances the actual steel welded structure is stronger than parent metal.

Drew, thanks for the update. Great work.

I don't understand a lot of what's going on here, but this is fascinating stuff. Would you consider doing an article for a publication like Double Gun Journal when the testing is finished? This seems like something worthy of permanent preservation.

This is the part of the blow-out piece that was bent almost 90 degrees. Unfortunately, I didn't take a good pic of the crack; on the right at the apex of the bend



This is a 20X photomicrograph after etching with 3% nitric acid/alcohol of the crack area



As part of the failure analysis, Adam is going to label the best images. You can clearly see the crolle pattern; iron is silver-white, steel grey-black. The black dots are graphite (carbon) that are from the cast iron. This crack does appear to be between the iron and steel thin strips that define the 'leaves' within the scroll (the twisted rod). Adam explained the lines at the lower right, but I forgot

This is the first published photomicrograph of a pattern welded barrel!!

And yes, there better be some articles from all this to off-set the almost $1300 for the failure analysis, $125 for MPI, $125 per radiography, and $50-$70 per tensile strength test. AND more photomicrographs if, as I suspect, radiography of a Syracuse Arms barrel at TEAM right now shows a crack.

It would take a significantly larger sample size to convince the gun industry as a whole, but for me this is truly groundbreaking stuff. Wonderful work, Drew. I feel lucky to be able to follow this as it unfolds.
-Will

Drew, I seriously doubt that you will find any of that mythologic interlaminar rust or orange lace in any of your samples. There would have been no red iron oxide on the surface of the iron and steel after they were heated in the forge to welding temperatures, and there would be no surface for exposure to oxidation once the layers were welded. Any thin scale formation that was not scraped, fluxed, or knocked off by hammering would actually be more resistant to oxidation than bare metal. I have seen flakes of mill scale up to 1/8" thick exposed to water for weeks before it gets even a tinge of orange color.

Fantastic stuff here! Thanks again for sharing it with us.

Indeed Keith. Unfortunately, once myth begins, it is repeated by the 'experts' over and over

Gerald Hunter “Don’t Blow Your Head Off!” Gun Digest 1962
Composite barrel metals are brittle, to begin with. The laminations were put together without accurate control, so the walls are not uniformly strong. Each joint of forge-welded metals is a potential pocket of rust or corrosion which holds together today but which by tomorrow may be ready to bust wide open.
Damascus barrels, once thought safe with black powder, are no longer safe! They’re getting older every hour and those hidden rusty – and rusting – areas are growing larger, the barrel walls thinner, and that hundred-and-first shot may blow ‘em up.

Another gun shop 'expert'. Found this on the internet, but the original source was not sited, nor the date. Anybody know this confused fella?

http://www.freerepublic.com/focus/bloggers/3018315/replies?c=18
Damascus barrels were actually superior barrels when new than many cold rolled welded barrels and hammered steel barrels. BUT, and it is a big but, over time the discontinuities in the Damascus barrel forging technique allows for internal corrosion to form in the hammered wire forging that that forms the Damascus barrels. This corrosion between the mechanical/welded/pressure joining of the metals that are at the core of all damascene metals is unavoidable, weakening the mechanical welded heat bonding because oxygen is incorporated in the joint by its very nature. . . starting the formation of rust at the creation of the barrel. With age, all damascene barrels LOSE considerable strength.
Barrels in that period were ALL proof tested with black powders that were far less pressure producing and slower burning than modern faster burning, higher pressure producing smokeless shotgun powders. Now add the corrosive nature of black powder and the even greater corrosiveness of the fulminate of mercury primers used during the useful life of most of these damascene barrels and its effects on accelerating the corrosion between the domains of the metal in those much more porous barrels. Shooting shotguns with Damascus barrels with modern loads is NEVER advised.
I am past manager of the Olde Sacramento Armoury and I was the appraiser and buyer of used and antique firearms for Simms Hardware (Sacramento) Gun Department — which was named #1 Gun Dealer in the United States in 1971. . . and was a qualified expert in the California Courts on the identification and values of Antique firearms back in the 70s. We labeled every damascene barreled shotgun a wall hanger, a non-shooting relic and instructed all sales people to instruct buyers that they were never to try shooting them as they were considered unsafe. We had several "educational pieces" on hand with blown chambers to show them what would happen if they tried. A couple of those looked brand new. . . and were made by some of those "top names" in gun making from London and New York. They still blew.

Boy the guys in the proof houses were not careful with their proof stamps. According to this expert they must have grabbed the nitro proof stamps by accident a lot of the time.

I couldn't resist...carry on.

No, don't laugh at him, not fair. He was world famous in Sacramento.

BTW, AFAIK Nitro Proof charges in UK were loaded with black powder for many years, and might still be so. Anyone know for certain?

Eug

Drew: Several times you have mentioned "cast iron". I don't believe cast iron was ever used in Damascus barrels. I think that you mean wrought iron, which is very low in carbon content and very ductile versus cast iron which is very high in carbon content and very brittle.

That is a neat micrograph Doc Drew, looks like a lot going on. Maybe they could point out what normal is supposed to look like, on the left? Those lower right, and other areas, lines, maybe grit marks from prepping the sample. Thanks again for putting the info out to see.

Tom: here is Adam's response

The microstructure with nodules (not flakes) of graphite looks like ductile iron (a form of CAST iron). The product has been wrought (rolled and twisted), but I would not call the starting product WROUGHT IRON as that generally describes iron silicates in ferrite and does not have the graphite structure seen here.

Craig: Adam is preparing images upon which he will indicate the important findings.
Hard to know what is 'normal' since no one has ever published photomicrographs of crolle Damascus before but everything to the left of the crack is normal. Adam is still working on those lines in the lower right.
He did show me a bunch of images with the yield stress indicators.

Lots more to follow gentlemen, but please keep those thoughts and ideas coming!

Thanks Doc Drew. Possibly, the parent material was not intended to be a form of cast iron. If those are graphite pockets, maybe those were inclusions that the damascus manufacturing process was intending to mitigate.

VERY interesting.

This was a good idea, Drew...

The graphite inclusions are illuminating.

I believe I'm correct in describing them as inclusions, correct me if there's a better term.

As uncombined Carbon, they contribute nothing to an Iron crystal structure and thus are a major flaw in the material.

It appears that the crack runs through a giant such inclusion, and that the area shown southwest of the crack where the inclusions line up would be another potential failure point.

I think we need to get it out of our heads that Damascus is 'steel'. It ain't. It's a composite structure. Even 'pattern welded steel' isn't a great description.

Just another quick take Shotgunjones. Maybe that gray area at the start of the crack is not carbon, it doesn't seem to etch the same. I'd wonder if the acid prep dissolves iron oxide, possibly a tiny pit, but not likely the origin of the crack.

The xray, micrograph and modern blacksmithing, I think show pattern welding to be more of a mono steel than series of connections. If this sample is a steel, in all likelyhood the carbon has migrated and evened out through the piece. The color differences may be other alloying elements besides iron and carbon.

A row of tiny carbon inclusions may not be a big concern. If this is a crolle pattern, that line may actually spiral through the material and may not be sitting as a sort of perforation line in the barrel. Just thoughts.

After some research, I think the starting material is best described as a 'ductile iron'.

References show it as a form of cast iron, but... and here's the interesting point:

It's also known as 'nodule cast iron', the main feature being Carbon nodules in the form of round congregations rather than flakes... the main result being the INHIBITION of cracks, because cracks are more likely to start at a sharp point than at a point with a radius.

This is interesting as can be. What a guy can learn with a computer...

It still isn't steel though... in steel the Carbon and Iron form an actual crystal, and there are variations thereof. A mono-steel I would expect would have to be heated above it's critical point to become homogenous, am I wrong?

Another question craigd, and I think you've done some work with steel and iron... why would not the excess Carbon 'burn out' of the iron during the welding process? It does so with steel during forging, and the forger has to limit the time carbon steel is held above a certain temperature to avoid this.

I'd suspect since iron and steel were forge welded together, they easily exceeded the critical temperature of the steel. That may not be really important here. The original smiths may not have had any intention to harden the barrel, and the carbon percentage in the steel, not the inclusions, may not be high enough to harden anyway.

Steve C. had a good comment about loss of material due to the forging process. It may be important to control times and temperatures, but I think most of the material might be lost as scale due to oxygen exposure. Maybe.

I agree that the intent wasn't to harden, in fact the 'ductile iron' was used to provide what it's name implies, ductility.

The failure modes, fluid steel vs. pattern welded, seem to show that the intent was achieved.

I've been following this thread closely. I wish that I could look over Adam's shoulder and ask him a bunch of questions.

I have been doing some micro analysis of steels myself. Well…… trying to. I have no formal training at this work and am trying to learn all that I can. I don't yet have Adam's experienced eye.

I have a damascus barrel section that I bought from Peter Dyson. Below is one of the images of it, that I shot through my microscope. Tomorrow, I will be spending a lot of time viewing steel samples that I have prepared. I'll try to post some comments and perhaps photos.

Steve, thanks for your knowledge and picture, it is great. Hopefully Drew will get more results and information.

Not just for us Damascus shooters, but to everyone who shoots old and older guns, this is one of the most interesting posts to come along.
Thanks.

I've spent a lot of time considering Adam's photomicrograph of the blown out barrel section and his analysis of the black spots being graphite nodules. I find the same anomalies in micrographs that I have taken of the old damascus barrel in my possession. But too, find them in micrographs of damascus that I have made from modern steels.

While I am NOT an expert in the field of micrograph analization, I have found that there are a number of reasons why black spots can appear in micrographs. They can be caused by the degree of surface prep of the sample, the effects of the type of etchant used and also the size of the material's grain structure. The micrograph posted of the blown out barrel section was taken at 20X magnification. The microscope in my shop is only capable of 20X maximum. I have found it very difficult to determine the exact cause of small anomalies at this magnification level. I hope that Adam will view the blown out section at a higher magnification level, to make certain of his analysis.

Regarding the analysis that the black spots are graphite nodules from the use of ductile iron, or any type of cast iron being used in the manufacture of damascus barrels; I am not yet convinced. I concede that the black spots appear similar to graphite nodules in the 20X image. However, the specific product named "ductile iron" was not invented until 1943. Ductile iron has magnesium added, which inhibits the graphite's growth directions, turning it into nodules. A similar graphite nodule formation can be created in gray cast iron, by heating it to 900C/1650F, and holding it at that temperature for 72 hours. I seriously doubt that damascus barrels were subjected to such a heat treatment process.

Nothing in my research of the historical manufacture of damascus barrels has indicated that cast iron was used. And my experience with making damascus steel causes me to doubt that cast iron could be utilized to weld damascus. Cast irons have a very high carbon content. The high carbon content makes cast iron what blacksmiths call, "hot short". If you heat a piece of cast iron and hit it with a hammer, it will shatter. It cannot be forged. I cannot conceive of trying to incorporate cast iron into a billet of damascus.

Again, I am not an expert and I don't intend to be argumentative. But my message to Adam, is to look closer. The use of cast iron in a damascus barrel seems improbable to me.

My research into damascus barrels has led me to a theory that the barrels were made up of a medium to high carbon steel, laminated with wrought iron. There is ample historical documentation stating that the barrels were made of steel and iron laminations. I base my theory of the iron element being wrought iron, from having read innumerable pages of old documents on iron making and usages, that were written contemporary to the manufacture of damascus barrels. In all cases that I have found, when the word "iron" was used, the material being spoken of was wrought iron. This was simply the common name used at that period of time. If cast iron was being written of, they used the words cast iron, gray iron, pig iron, etc. If they used the word "iron", they meant wrought iron.

Wrought iron was produced from cast iron, by a process of heating the metal to just below the melting point. An air blast was directed at the surface of the iron, to burn off the carbon content and most of the damaging impurities. The iron was maintained in a semi-melted plastic state and constantly stirred to mix in the iron oxides that formed on the surface of the iron from the air blast, and also silica from sand and limestone used as a flux. This admixture being basically an iron oxide bearing glass. This constant stirring of the material is where the name "wrought iron" comes from. Wrought meaning, hand worked. Once the iron was sufficiently decarburized and thoroughly mixed, a ball of the material was removed from the furnace and taken to a power hammer, or press, where the ball was forged into a bar. During forging out the bar, the globs of iron/silica are stretched out into strands, lengthwise of the bar. This first bar was often cut into pieces, restacked and forge welded, then drawn out again. The restacking and welding would reduce the size of the strands of silica and also force out some amount of it. Depending on the intended end use of the material, restacking and welding could continue until the material was nearly pure iron. A common product of the foundries was called merchant bar. Merchant bar was fairly high in silica content. The intention was that the end user could restack and weld the material to suit their needs.

Below are three micrographs that I took of a piece of wrought iron from a anchor chain link. You can see the strands of silica in the side (first) image, running lengthwise of the bar. The micrograph of the end of the bar, shows the black spots created by the ends of the silica strands. Note the image of the entire end of the wrought iron bar. The lighter hued lines are the edges of the restacked bars that were forge welded to make up this single bar.





I have a section of damascus barrel tube, that I purchased from Peter Dyson. This barrel tube is in its as forged condition. It was never finished out. It still has the chemise inside it. I sawed part way through the tube and then broke it off. Below are two micrographs of the end of the broken section. The layers of steel in the damascus are very fine grained and a flat gay color. The layers that I theorize to be wrought iron, are very course grained and include black spots; which I believe to be silica strands. The chemise appears to be of nearly pure iron. No silica strands are evident in the chemise at this magnification.




Below is a micrograph of an etched section of the damascus barrel. This image shows black spots in both the steel layers as well as the wrought iron layers. The above image of the broken barrel section does not indicate the presence silica strands, or graphite nodules in the steel layers. I can only assume that the black spots were created by the effect of the etchant.



Below is a combination of two micrographs of the ends of damascus bars that I made. The steels in this damascus are 1084 and 1018. The left image, is of the damascus after thermal cycling to reduce the size of the steel's grain structure. The right image is of the same material, after heat treating to create a spheoridized grain structure. Spherodized grain, is a very large structure. Notice the differences in how they etched. Also notice in the left image, the thin lines. These are decarburized weld lines, where the damascus billet was restacked and forge welded. This area etched less, because of the lack of carbon. In the right image, the weld lines are nearly invisible. During the heat treatment to spheroidize the material, the extra time at heat allowed carbon to migrate back into the decarb areas.

As always, thanks so much Steve. We're all in uncharted territory here, and the more guys thinking, and willing to contribute, the better!

I've previously posted that is someone would please whack off the end of their Damascus demonstration rod (science will thank you ) METL can separate the iron and steel strips and tell us exactly what they are.

In part the silica was coming from the coke used in the smelting furnaces. This was a major concern for the damascus barrel makers.

Pete

Thanks Guys,

Please understand that it is not my intention to disparage Adam's work. I am trying to learn and I have questions about how to understand what you are viewing in these images. The more that I look at micro photos and realize how many factors can affect what is seen, the more questions I have.

Did some work today to try and find a comparison to the layers that I theorize to be wrought iron in my broken off barrel section. (The image posted earlier) The metal in these layers has a very large crystalline appearance. It's hard to tell in a photograph, but the crystalline structure sparkles, like diamonds. The only comparable sample that I have looked at is etched 1018 steel. Etched 1018 has a very similar sparkly, crystalline structure. However, the broken barrel piece has not been etched. Then, there is the black material, that I believe could be silica. But, it looks like a LOT of silica. I'm surprised.

Image of etched 1018 steel, below.



I broke a piece from the sample of etched 1018 steel and looked at it under the microscope. I did not etch the broken area. It appears to be a fairly small grain structure. Not at all like it looks when etched. Notice in the image, the lines similar to those seen in the blown out barrel section. Perhaps a product of stresses induced during the forceful destruction??



I then broke a piece from the wrought iron anchor chain sample. Again, no etchant applied. VERY different than the barrel piece. It almost looks like it has hair. Notice the rather large inclusion, at about 10 o'clock.



Result at the end of the day…………. More questions.

Thanks for all that work Steve.

You're getting a standing ovation here...

Thanks also Steve. Good stuff.

I wonder if the lab did find graphite inclusions in the barrel, that it made for a higher carbon content, but the carbon available to form steel might be closer to that 1018 that you looked at. Possibly not a true medium to high carbon steel component of the damascus.

It seems like the materials used were known to have flaws, so I wonder the repeated drawing, twisting and welding was to minimize the dimension of inclusion and disperse them. In Doc Drew's micrograph, if those are carbon inclusions, they seem to be of a generally small size and separated from each other. There doesn't seem to be any obvious clusters of graphite or even larger inclusions like shown in your wrought picture.

Sorry, have to do it......

Sooo, what would be the better choke for a furnace?

Upland, not industrial district...over pointers?

Seriously though, that is some amazing information and imaging, I hope everyone continues to contribute to this in a factual, open minded way as it has been very enlightening.

Best,
Mark

Steve, that's a very interesting contribution to the discussion. But I doubt if there is actually more than a trace amount of silica in finished 1018 steel. The amounts in wrought iron would typically also be small, as most of the silicon content of the ores is greatly reduced by the addition of limestone or lime to produce slag. Here's some information I found on silica content in iron:

".... Silica (SiO
2) is almost always present in iron ore. Most of it is slagged off during the smelting process. At temperatures above 1300 °C some will be reduced and form an alloy with the iron. The hotter the furnace, the more silicon will be present in the iron. It is not uncommon to find up to 1.5% Si in European cast iron from the 16th to 18th centuries.

The major effect of silicon is to promote the formation of grey iron. Grey iron is less brittle and easier to finish than white iron. It is preferred for casting purposes for this reason. Turner (1900, pp. 192–197) reported that silicon also reduces shrinkage and the formation of blowholes, lowering the number of bad castings...."

It's interesting to note that silicon promotes the formation of grey iron which is "less brittle and easier to finish than white iron". So the presence of some amount of silica in the wrought iron used in Damascus could be either a curse or a blessing depending upon the percentage of silica content. We probably won't know what's in the amalgam of iron and steel used to produce old Damascus without an actual analysis done by a metallurgical lab. I worked in an integrated steel mill for several years after college and recall sending samples to the met lab during a heat and getting accurate results in short order, down to small fractions of a percent. Then the melter could add ingredients, or alter carbon content by blowing oxygen. They used Infrared spectroscopy then, and I wouldn't be surprised if mills use NMR now. The final analysis followed the product to end finishing and directly to the customer. Looking back, I wish I'd paid more attention and asked more questions, but often, the great object was simply not getting burned alive.

The introduction of coke to the smelting process was a later development. Initially the Liege makers were up in arms because they felt it introduced silica and the barrels just did not look right to them. A long search ensued. They tried steel from every source they could. Eventually Cockerill, "the" maker of steel in Belgian, bent to their desires and changed. What forces were brought to bear on Cockerill is not clear. He certainly did not 'need' their business.

Pete

Is choke the same as coke in smelting ?

Steve, are you accurately using the term "broke" to describe your method of exposing the inside of your sample? If you are actually "breaking" the material then I don't think you can accurately diagnose the exposed edge.

Suppose you wanted to examine the inside of a marshmellow. I don't think forcibly tearing the marshmellow apart would yield an accurate image of what the inside looks like when leaving the marshmellow factory.

Right, wrong, or am I missing the point?

Thanks for the appreciation guys,
Perhaps I should explain the purpose of my work with the microphotography. I am searching to find a combination of steels to use for making damascus gun barrels. I am hoping that these steels will also be capable of heat treating to make knife blades. I have chosen 1018 steel as the replacement metal for what I believe is wrought iron in old barrels. I have welded several billets of damascus, having the 1018 layered with a different high carbon steel in each billet. The billets were drawn out into 1/2 inch square rods. I am subjecting the rods to different heat treating processes, which are the same as I will be doing to the material if used for a barrel or knife blade. After each heat treating process, the rods are etched with ferric chloride to see the result. I will also be etching these samples with a couple of different acids, as well as testing how well they are capable of taking browning and bluing. I have a lot of tests yet to do.

To better understand the results from my testing of these materials, I am studying the chemical reaction of different acids and metal salts (like ferric chloride and copper sulfate) on steel. As etchant solutions and bluing/browning chemicals are all types of acids, or metal salts, I feel that it is important to understand how they work, in order to be able to get predictable results in finishing the damascus. Acids and metal salts effect steel in ion exchange reactions. Essentially, like hooking a microscopic battery to the steel. My testing suggests that the "connections" for these electrical exchanges, are the edges of the steel's grains. The size of the steel grain structure appears to affect the number of electrical connections available for the ion exchanges to occur. This can be seen in the image that I posted earlier of the damascus rod of 1084/1018 steels. The finer grained rod etched very uniformly, because of the many connection points. The rod with the larger spherodized grain structure etched very coarsely, because the contact points for the exchange of ions were farther apart.

As there was no specific heat treatment utilized to control the size of grain structure in old damascus gun barrels, this could well be the reason why barrel refinishers sometimes will find a damascus barrel that does not finish well. The acids used for coloring the barrel cannot effect a uniform bite on the steel, because the grain structure was not refined after forge welding.



I am fairly confident that the "steel" component of old damascus barrels was actually high carbon steel. At that period in time, they fully understood what high carbon steel was and were capable of producing it efficiently. I also base my analysis of the material on its reaction to etching with ferric chloride. It etches and colors very similar to the 1084 steel that I use for knife blades. The reaction of steels to etchant solutions, can tell a lot about the alloys in the steel and also help to display the grain structure.



Agreed. I am using analytical 1018 steel. So, I know there is only a trace amount of silica in it. The fact that the etched 1018 sample appeared to have a similar large grain structure as the metal in the old barrel was what caused me to test the 1018 by breaking it. Note that the 1018 sample had undergone the same spheroidizing heat treatment as my high carbon steel samples. I was surprised to see that etching the 1018, caused it to appear as if it had a large grain structure. Breaking the 1018 sample, indicates that it does not have a grain structure as large as suggested by the etching. The crystalline appearance of the etched 1018 was solely a function of the etchant's effects on the steel. Why; I do not yet know. Another reason to get a better understanding of how etchants effect steel.



I think most will be more familiar with the spelling as coke, rather than choke. Coke (fuel), a solid carbonaceous residue derived from destructive distillation of coal.
Pete, I think you may be confusing silica with sulfur. Silica is not a major issue in steel. The inclusion of silica in wrought iron actually makes it easier to forge weld, causing it to be somewhat self fluxing. Sulfur is very damaging to steel. Too, sulfur will inhibit forge welding. Blacksmiths who use coal forges always seek out low sulfur coal. High sulfur coal in the forge can prevent forge welding.

Do you know where Cockerill got the iron ore for their steel making? I found an old book on mining, that has the chemical analysis' for ore samples from mines around the world. If we have information on where Cockerill obtained ore, we may be able to find the analysis for it and learn more about the alloys in the steel produced.



I did actually break the samples. It is an accurate way of exposing the grain structure in hardened steel. I have examined hundreds of broken knife blades, to see if the material was properly heat treated to reduce the grain size after forging the blade to shape. It is not an easy method to employ with soft steel. Hardened steel will snap off cleanly, leaving a surface that is easy to analyze. Breaking soft steel can leave so much structural damage, that there is often only a small place on the sample surface to analyze. Takes some experience to know the difference between grain boundaries and structural damage.

Duh! My stupid typo.

Thanks,

Pete

Thanks for your time Steve. I hope follow up thoughts are okay, not questioning your research and experiences. I'd suspect if wrought iron were used as one of the components, that the overall carbon percentage would even out to at best to what might be considered medium. Also, I think etch appearance of modern steels might be affected by added manganese, that would be interesting to know what amount may be present in historic barrels.

I've also noticed that barrel bulges are a common type of historic and modern barrel failure. There are many historic accounts of bulge repairs by hammering down and refinishing bulges. Even today it's a viable repair possibility and tools for slowly raising dents are available. My take on the mechanism of plastic barrel failure and the possibility to cold form it back may(?) be more generally successful on low carbon steels.

Thanks again for all your time, and thoughtful explanation, Craig

Am I correct that damascus barrels were not heat treated? Would that make them "soft" by comparison/classification to a damascus knife?

I also wonder what house manufactured the barrel sample you have in your possession? Was it of high quality, or one of the "belgian clunkers" from a substandard manufacturing process? I thought I was understanding this process until you came along with the other micrographs. I am still trying to understand the similarities, thus my question and comparison to tearing a marshmellow. A crude comparison, but one I thought my mind would understand.

When you say soft metals are harder to break, is that the result of the grains essentially stretching? Ductility?

Pretty amazing how many people on this board know about iron and steel. Impressed with the knowledge.

Follow-ups are quite welcome! I fear that I have nearly hijacked this thread. My intentions with my first posts, were to point out that there are numerous ways that anomalies can be created in micrograph images and that at 20X magnification, it can be very difficult to make a determination of exactly what they are. Didn't mean to get too far into my work. I guess as long as it pertains to analyzing old damascus barrels, it's still good.



CORRECT! Carbon migration is scientifically proven. Once the forge welds are solidly completed, the carbon seeks to find a balance between the laminated layers. I have some documentation that suggests the rate at which carbon will migrate between the materials. It is a time and temperature related chemical reaction. The higher the temperature, the faster the carbon migration. However the caveat to this, is the alloying content of the steels. Certain alloys will, and can be added to the steel for the purpose of controlling the carbon's molecular bond within the iron matrix. Obviously, this will affect the rate of carbon migration.

I believe that the overall carbon content of old damascus barrels will fall in the .35 to .40 carbon range. This is below the carbon content that would heat treat well for things like knife blades, but is just enough to affect the steel's grain structure.

Jumping forward to Jawjadawg's question about damascus barrels being heat treated; I do not believe that there was anything comparable to a hardening quench and tempering process done to them. However, I have read in several writings of the cold hammering of barrel tubes after welding. Greener states that this hammering “greatly increases the density of the metal” and was done to the best barrels. The tubes were not actually “cold”, but in blacksmith terms, at a heat that was too cold to effectively move the steel under the hammer. This would be from around 1400 degrees F, down to a temperature of about 900 to 1,000 degrees F. So they were aware that the process created barrels that had a better finished appearance. It appeared to them that the steel was more dense, but actually, it was simply of a smaller grain structure. The hammering that was done to the tube was unnecessary. It was the repeated heating and cooling of the tube that affected the grain structure.

This heating and cooling of the steel is called thermal cycling, or normalizing. We knifemakers do this to all of our forged knife blades; or, it should be done. The heating to low red heat and cooling in room air to a black heat is repeated three or more times. I am convinced that this is exactly what the barrel smiths were doing during the cold hammering of their barrel tubes.

Normalizing will not soften steel to the dead soft condition of being fully annealed. But fully annealed steel will not etch well, because it causes lamellar banding of the pearlite grain structure.



I have heard from many damascus smiths, that manganese will cause steel to have a darker appearance with a ferric chloride etch. However, my recent testing has not proven that conclusively. It could be that the etch coloration is more closely related to the grain structure. We knifemakers know that hardened steel etches darker than soft steel. If we make knife fittings out of damascus, we have to run them through a complete heat treatment, just like a knife blade, to get them to etch well.

I am acquainted with about 100 of the finest damascus smiths in the world. We all know how to go through the steps that we have learned, to make our damascus come out looking nice. Yet, none of the smiths that I have talked to can explain the chemical process that makes this work. That is the reason for my testing. So far, I have only been compiling test results. I have not had time to analyze them fully. At this point, I have many more questions than answers.



The barrel tube that I have is of Belgian manufacture. It is of two iron Crolle pattern. This I find a bit unusual, because most of the Crolle pattern barrels that I have seen were made of three twisted rods. I expect that this tube was intended for a lower grade gun. However, I view the workmanship of welding it to be superb. I doubt that they intentionally made "clunker" barrels. Some may have been made with the intention of keeping labor costs down; like perhaps with the barrel that I have. I expect that barrels of complicated damascus patterns, like Bernard and chain, were more likely to be welded by experienced smiths, due to their skill of uniform manipulation of the material. Barrels were probably graded after finishing and etching to display the damascus pattern. Barrels with very uniform patterns would be saved for best guns, while less perfect patterns were sold for use on lower grade guns. I doubt that the steel and iron used for barrels, were different for best barrels and lower grade barrels. The steel and iron would not be the major cost factor in barrel making and it would not be cost effective to run different grades of material. Too, it would be best for the barrel welders to always work with materials that they are familiar with.



Yes, the ductility makes breaking soft materials very difficult. I broke the piece of 1018 three times before I felt that I had a surface that I could analyze. I wouldn't have tried it at all, except that I was trying to match how the barrel material was exposed.

Thank you again, for taking the time to answer. I was asking about the maker of the tube because of the widely held belief in the vintage gun community that significant variations in quality exist in the pattern welded gun market. The term JABC is used to identify guns which are not usually even considered for safe shooting by members of the vintage gun community. I think it is safe to say that tubes produced by Henri Pieper are considered near the top of the pile in terms of quality, and therefore, consider more likely to be SAFER for shooting today.

Why the difference in quality? I suspect that the main difference is the manufacturing process (duh!) and perhaps a difference in materials and "additives". Sort of like the difference between Coca-Cola and a generic cola, or McDonald's French Fries and the ones you might buy at the gas station deli stop. Pieper didn't tell the rest of the Belgiam gun making guild his trade secrets, but I've read that the top American gun makers all sourced their barrels from a select few providers, Pieper believed to be among them. Was that strictly a cost driven decision, or had Pieper and the other "quality" tube producers demonstrating superior quality (safety) to the marketplace?

I believe Drew's study has the potential to alleviate or perhaps begin to change the way the shooting community views pattern welded barrels, depending upon the depth of the research. It might also demonstrate that pattern welded barrels shouldn't be kept in use. Who knows? Either way, I do not think the outcome of Drew's testing and analysis will do anything to change the view of anyone regarding the safety of shooting those guns we refer to as "JABC". I believe that the experience of the shooting community has demonstrated that JABC barrels are far more likely to pose a safety issue. For that reason, I was interested in understanding a little more about the comparison of the two materials - Drew's and the one you imaged.

The visible separation of the materials within the metal was far more evident in your sample than in Drew's micrograph. The basic point of my question is pretty simple...WHY?

Do we have two apples cut open, or is one of them an orange with understandably different grain structure?

I've wondered if the mentioned cold hammering, in the context of a low carbon steel, was a form of work hardening. Or, the perception of increased density by smiths of the era.

Maybe(?), after the tensile tests a 'typical' damascus barrel sample could be sent off for spectrometer chemical analysis. Say three or four samples off the same barrels, just to get a feel for how different or similar readings would be off same barrel. I'd spring for it if Doc Drew wanted, and if his lab wouldn't do it, maybe even the local Fastenal might.

The experience of good smiths seeing a forming pattern even if it wasn't visible was my thought process about the barrel grinders. I was just suspecting that there were some barrel grinders that could size up a blank better than others, and had a better sense of where the pattern was before it was finished. I wonder if more time consuming patterns were walked over to grinders that had the knack, just to give things a better chance to come out as hoped.

Pieper supplied "Finest Damascus" for Remington Model 1894 EE Grade guns and also "Oxford 4 S.J." The barrel makers were so skilled that they could produce this



Ernest Heuse-Lemoine (1834-1926) from Nessonvaux was a major barrel maker in the Vesdre Valley maintaining agents in London, Birmingham, and New York. Every 3 years he would travel aboard and upon his return, would be met by a band in celebration because he always came back with more orders than his own firm could handle. He would then distribute some of the work to smaller barrel makers. Gaier states that Heuse-Lemoine supplied damascus barrels for at least 50 years to US makers, and that he invented the names of "Boston" and "Washington" damascus especially for the American market.

Leopold Bernard barrels were highly regarded, but about every Belgian maker also produced Bernard pattern barrels
https://docs.google.com/a/damascusknowle...iP3FP0fXb0/edit

It is very likely that the U.S. makers used the same sources for 'rough forged tubes'. More infro here
https://docs.google.com/a/damascusknowle...s66tEXntqw/edit

Bottom line: barrel quality is best judged based on the overall quality of the gun
https://docs.google.com/a/damascusknowle...8WMIMkdKr0/edit

I suspect the JABC Twist barrels will have a lower tensile strength, but we'll see

I realized that should have stated clearly in yesterday's post, that I do not know the maker of the old barrel in my possession. I purchased an unfinished tube section from Dyson. I believe it to be from the mid area of a barrel. It does not include the breach area, where it would have held a maker's mark.

My little brain can't keep up with all of the manufacturer's names and dates. That is the realm of many of you fine Gentlemen. My knowledge is primarily of the technical aspects of barrel making.



The barrel specimens are not so much apples and oranges, but the micrographs are. Adam and I were prepping our samples to view entirely different properties in the steel. Adam used a very mild, nitric acid etchant solution. His use of the etchant, was to clean the steel of surface oxidation and to lightly color the metal. His purpose for viewing the sample was to examine structural damage. I am using a much stronger ferric chloride etchant solution. I am doing a deep etch, to replicate the finishing process that I use on damascus. I want to see what these test steels will look like if I make items from them.

There are many acids and metal salts that can be used to etch steel. Each will cause a different type of decomposition of the steel, and/or chemical change to the steel's surface. Etchants are chosen to prep test samples, depending on what it is that you are trying to determine from the analysis. The nitric acid that Adam used and the ferric chloride that I used, cause entirely different reactions with the steel.

Another variation, is the surface preparation of our samples. Adam was viewing his sample for structural damage. I expect that he did no finishing of the material before etching, as he wished to view how the material was ripped apart. I am sanding my samples before etching, to create a flat surface. The manner and quality of surface preparation, is critical to the ability to view specific qualities and anomalies in the material. This is partly why I question Adam's analysis of the chemical make-up of his sample. How can he look at an irregular surface and know that he is viewing carbon nodules and not artifacts of structural damage? I'm sure that Adam has a much more trained eye than I. So, my questioning of his analysis is more about learning, than arguing.



Some amount of work hardening from cold hammering is almost certain. However, reheating the steel for another round of hammering would soften the steel again.

Grain structure in steel is visible to the naked eye. Heat a piece of high carbon steel very hot, quench it and break it. The grain structure will look very large and crystalline. Take the same piece of steel and heat it to a dull red and allow it to cool in air. Repeat the heating to dull red and cooling in air three times. Then, bring the steel to a proper austinizing heat for hardening and quench it. Break the piece and look at the grain structure. It will have a dull, flat gray appearance. It looks more dense. This thermal cycling of the steel is called, normalizing.

There is no way to know for certain why the barrel makers perceived that hammering on cold steel caused it to be more dense; but I have a theory. With everything that is forged, the last thing you do is straighten it. Straightening is done at a lower heat, so the hammer is not actually moving material at the point of impact, but affecting the bending of a larger section of the piece. I can imagine that after cold hammering to straighten a crooked barrel tube, they noticed that the steel looked more dense. The more crooked the tube and more cold hammering required to straighten it, the more dense the steel appeared. They thought that the cold hammering was compacting the steel, not realizing that the repeated heating and cooling cycles were refining the grain structure.

This same myth existed in the blade forging community until fairly recently. When I started making knives, the old makers told us all about "edge packing". We were taught that the last thing you did when forging a blade, was to cold hammer along the edge of the blade to pack the steels grains together. About 20 years ago, someone finally put their thinking caps on and considered the fact that steel is a solid and you can't compress solids. Normalizing the blade's steel is now taught as a critical aspect of making forged blades.



I'm sure that the more intricate patterned barrels were only entrusted to experienced grinders. But, you have to consider exactly what the grinder's job was. After forging, the barrel tubes were sent to the boring shop. After boring out to final dimensions, they went to the straightening shop, where they were actually bent to make the bore straight. After the bore was straight, they went to the grinders. The grinder's job, was to grind the outside of the tube concentric with the bore and to remove the material required to leave the barrels walls the correct thickness and taper. If he varied the amount of material ground from the tube to affect the damascus pattern, the wall thickness and taper would be changed. This would even cause the finished gun to balance differently. The grinders job was primarily to grind the barrel for strength and balance. I have no doubt that the art barrels, like the ones with words welded into the pattern, were pulled from the grinding wheel and lightly etched to reveal how the pattern was developing. I expect that concessions were made for the balance of the gun, to accommodate these works of art.

The task of placing the damascus pattern where it will be properly developed from grinding, was entirely that of the barrel welder. If you have watched the silent video that Pete sells, you have seen the barrel smith checking the outer dimension of the barrel tube with a gauge. The smith knows that with the thickness of material he is working with, by forging the outside to a specific diameter, there will be sufficient material to bore the tube, plus leave the correct amount of material on the outside of the tube to develop the damascus pattern during grinding.



I am curious what the testing will reveal, but I expect that there will be little difference in the strength of JABC barrels. These barrels still had to pass proof. It would not be cost effective to make barrels that risked not passing proof. Too, the barrel maker's reputation depended on not having barrels blow up in a gun owner's hands.

I still maintain that the barrels that you Gentlemen refer to as JABC, were barrels of simple damascus patterns that required lower labor costs to make, and/or had irregular damascus patterns. I will be fun to see!!

Steve may be proved correct regarding pattern welded barrel strength. Both English machine forged Skelp (Twist) and Belgian Pointelle' Twist were in the middle of the pack in the 1891 Birmingham Proof House Trial
http://docs.google.com/a/damascusknowled...TEK8OtPYVA/edit

Good stuff to know AISI 1084- close to the AISI 1090 steel that Ka-Bar uses and did even in WW11 for their famous sheath knives adopted by the Army and USMC in 1941-- Wonder what the steel analysis of the Fairborn-Sykes "Commando" knife used by the Limey Force 316- see "Bridge On The River Kwai" etc- later the British Royal Marine Air Service was- different shape, no fuller. full hilt- great fighting tool for "up close and personal" work indeed.

Progress report and another image; 20X Nitrol etched



Steel above and below, with iron in between.

From Adam:
The globular shape of some of the inclusions looks like molten (cast) material, but with our better prep technique and some EDX work the inclusions appear to be mixture of silicates, oxides, and carbon (not just graphite). This is more indicative of wrought iron (or what we call wrought iron today). The chemical analysis we measured also had 0.01 weight percent C and I would expect to see something closer to at least 1.5 weight percent if it were truly cast iron (by today's standards). I suspect they used whatever was at hand that they called iron (wrought or scrap perhaps). I wonder if perhaps they used the terms "steel" to denote an alloy with controls on the individual elements and "iron" to indicate whatever else that was iron based.

I'm meeting with Adam again Weds.

Drew,

Hope your mission trip to Guatemala was productive and rewarding!

This information from Adam is very interesting! I question the carbon content stated in your text. 0.01 carbon content would be virtually nil. Is it possible that the decimal point is off one place? Maybe the correct number should be 0.1?

Still, I am surprised that the average carbon content is so low as 0.1. Though, I would not argue with the analysis. My SWAG estimate would have been 0.3 to 0.4.

From what I have read in old metallurgical books, they were quite adept at controlling the carbon content in steel at the time damascus barrels were made. 0.5 to 0.6 carbon content is sufficient for making springs and cutting tools. They were aware of the difficulties of heat treating hypereutectoid steels, so typically avoided making steel with more than 0.8 carbon content. Given this information, I have assumed that the carbon content of the "steel" element used in gun barrels to be around 0.6 to 0.8 carbon content.

Greener wrote that the steel to iron ratios were typically at least a 50/50 mix in English made barrels. And usually, the steel percentage was higher than the iron. Assuming a 50/50 mix of steel and iron, and knowing that carbon migration would happen at the elevated temperatures of forging, I would have made the guess that the average carbon content of gun barrel steel would be in the 0.3 to 0.4 range. This however, may only apply to English barrels. Without information on Belgian barrel steel, it may be possible that the Belgian steel could have been lower in carbon content. It would be interesting to see a chemical analysis on an English barrel, to see if the average carbon content is higher.

I was kind of wondering about that decimal point also. Great picture also Doc Drew, possibly higher magnification than 20x. Do the folks at the lab think that's a view of the grain in the steel component.

Seems most of Adam's comments were about inclusions, with none of them likely to contribute to the strength of the barrel. I'd still wonder if the labor was put in to overcome the shortcomings of the material.

Maybe, mono steels needed to be reliable and cost effective before taking over. Might be too that alloying became more important than just upping the carbon percentage.

Drew,
A.H.Bogarbous in his book, "Field Cover an Trap Shooting", pages 426-431, records a visit to W&C Scott In which he comments on Scott's method of manufacturing Damascus barrels.We learn that the key ferrous ingredients used were old coach springs and rusty anchor chains. This would likely result in a mixture of Wrought Iron and a carbon steel with a C content of approx.;0.5%.The report also states that following extensive sorting and cleaning of the scrap the net yield of good metal retrieved for best barrels was 20% and that the resultant cost was very high at 70 - 80 pounds per ton.
Based on this report it would seem reasonable to suppose that English Damascus made from Scott,s feed stock would have a carbon content in the .2-.3% range
I am also aware, that faced with soft barrels ,[low carbon content] the old barrel makers quote, "densified" the barrels by cold hammering to increase strength and hardness. Which today we realise had the effect of raising the yield point[but not the ultimate strength] and hardness of the barrel material.

As always, thanks to everyone for the thoughtful posts.
Dennis Potter graciously provided two 3 rod 'Oxford' Damascus barrels from English gun makers for tensile strength testing, but the tubes are very likely of Belgian manufacture.

Another valuable meeting with Adam. What follows is the non-technical non-deep thinkin' Baptist version

1. Adam confirmed the .01 carbon weight percentage.
2. The barrel did not fail by an intrinsic defect but by a single high pressure event ie. NO LOW CYCLE FATIGUE and NO INTERLAMINAR RUST.
3. The inclusions are slag and when lined up, can be the site of micro-fractures. but did not seem to contribute to the barrel failure. The linear structures (mostly in the iron) in the image above were likely formed as part of the rolling process.
4. The barrel does act like a monometal; although the iron bands have greater ductility than the more brittle steel bands. Composition analysis shows significant blending of the base materials.
5. The fracture lines did not, for the most part, follow weld lines.

Thanks to AmarilloMike, I've been reviewing Burrard on barrel bursts and feel confident that he would diagnose the event that destroyed THIS barrel as from an obstruction.

Very nice.

The old major would likely be pleased.

His work proven beyond reasonable doubt near 100 years later using techniques he never dreamed of.

Well done Drew.

I have said it before & I'll say it again;
"IF" you want to learn about Shoguns, don't "Read" Burrard, "Study" Burrard.

Thanks for the updates. I would have originally guessed the different images might have shown more welding flaws and inclusions, but they really do look good in your samples. Though they could detect a difference between the iron and steel, once welded and twisted, it does seem like the working barrel behaves like a monosteel.

Looking forward to any tensile strength comments you're able to share.

A 500X of the inclusions; silica, carbon, junk



Burrard was a master, but the second edition was written in 1948, before compression formed hulls, polyethylene wads, the widespread use of reloaded shells, the industrial application of piezoelectric sensors for pressure testing, scanning electron microscopy (SEM), composition analysis by X-ray Photoelectron Spectroscopy (XPS or ESCA), Energy Dispersive X-ray Spectroscopy (EDX or EDS), Ultrafast laser spectroscopy, and likely lots of other stuff I don't understand.
He did mention the industrial use of MPI and radiography dating to the 30s.

Certainly. But it does make his statement that a ring bulge always indicates an obstruction all that much more remarkable.

That sweeping conclusion, circa 1930's, has yet to be proven wrong.

Microphotograph, scan, dissect, analyze as you wish.... we first saw pretty well defined evidence of a bulge just in front of where this barrel failed. We 'speculated' it was an obstruction based on Sir Maj. GRB's ancient teachings.

Drew, at his own expense and as a service to us who wish to use old guns in a safe manner, has confirmed that the old master was indeed correct.

This is a significant contribution to the art and science and history of the shotgun. Bravo again.

Drew,

Thanks again for the additional information! I'm quite surprised at the low carbon content. But as a buddy of mine often says; "One test result is worth a thousand "expert" opinions."

The linear structures are typical of the silica strings that are found in wrought iron. Globs of silica in the iron as it comes out of the furnace, are drawn out into strands when the material is forged and/or rolled into bars.

I'm still a bit perplexed by the inclusions in the "steel". I expected the steel to be a cleaner material. Going to have to think about that a while………

Steve: As we discussed yesterday, I'll be sending you and our mutual friend in Nevada the full Failure Analysis, the unused barrel segments, and what is left of the barrels used for tensile strength testing. We should have about 10 3 and 4 iron crolle Damascus pieces to play with, and the only limit to the investigative possibilities is our curiosity and rapidly being depleted bank accounts

Drew, the larger pieces of junk in your 500x photomicrographs looked similar to some photomicrographs of steel mill scale I was looking at. Mill scale could certainly be a likely candidate because it is by far the most common impurity that is found in a steel mill. Another slice just a few thousandths away might well have been much cleaner and more homogenous. Scale itself has many and varying components, dependant on the alloys in the steel. Hence, the varying appearance under magnification. Ferrous oxide, various other iron oxides, magnetite and hematite are prevalent. I examined a very thick piece of scale last night, about 3/16" thick. Surprisingly, it was very different, from the inner surface that contacted the steel, to the outer surface that was in contact with the reheat furnace atmosphere. So just the orientation within a steel sample could possibly make it look like different animals. The inner part was dull and much more granular while the outer part looked smooth and shiny, almost like blue-black glass. The outer skin had a noticeably stronger attraction to a small magnet too.

I'm sure some would look at those photos as proof that Damascus is full of flaws and weaknesses, but rolled-in mill scale is probably just as likely to be found in early fluid steel barrels.

I'm thinking that's a 'typical' sample that the lab ran into on this barrel. At 500x, I'd think those inclusions have been effectively managed. Since it came from the barrel, that sample has been drawn down to a tiny percentage of the raw starting material.

New inclusions might be introduced, but that picture does not appear to be at the surface or near a weld. Chances are those inclusions were larger, but may have been reduced and dispersed by the extensive forging.

Here is a 50X of the inclusions Craig and Keith



I do not believe Adam has found any voids, contrary to Damascus mythology

Drew,

Do you need a set of lower grade Belgian twist barrels? I happen to have one, I was going to use it to test refinishing processes. It's one of those that are stamped "Laminated Steel" but I think it's really twist. Would you like all or part of it?
Ken

Thank you Ken, and PM sent.

BTW: I would very much like to include Armory Steel used by American Gun Co./ Crescent Fire Arms Co. and Meriden Fire Arms Co./ A.J. Aubrey in the tensile strength testing.

METL Metallographic Analysis is in, and here's the short version. I'll let y'all know when/if the long version gets published

I believe the burst was caused by an obstruction, likely the shot wad from the previous shell, lodged in and just past the forcing cone, caused by a light powder drop in reloading and incomplete combustion from the very low temperature. There may have been a pre-existing bulge also.

1. Did the barrel fail related to low cycle fatigue? NO

The fracture surface exhibited a mixture of ductile overload (plastic deformation with both tensile overload and shear) and transgranular cleavage indicating a ductal failure mode with rapid failure. The cleavage failure appeared to form preferentially in the steel component. No evidence of fatigue failure was observed; there were no striations on the fracture surface.

2. Did the barrel fracture at a ribband edge weld, between iron and steel rod welds, or within a rod? NO

The fracture did not appear to trace along the ribband (spiral) welds. Some cracking was seen along the individual bands within the crolle pattern, but this was not always the case.

3. Did the barrel burst related to interlaminar rust, inclusions, voids, or embrittlement? NO

No evidence of embrittlement was observed. There were a large number of inclusions but there was no apparent fracture jumping from one inclusion to another. The composition of the inclusions was predominantly silicon, phosphorus, and sulfur ie. slag.
No voids or interlaminar rust were observed.

While the microstructure was banded, and the bands had different grain size, inclusion content, and inclusion form (globular in the iron and linear in the steel)... “the overall material appeared to be a single piece of metal...(without)...microstructural defects.”

Chemical composition was similar to AISI 1005 low alloy steel. The low range of tensile strength is 40,000 psi, but may be heat treated to much higher numbers.

Hi Drew,

Thanks for the summary. It's reassuring to know that these barrels are basically sound as opposed to all of rhetoric over the years about being an accident waiting to happen. It is interesting to note that failure did NOT occur at the presumed weak points.

Phil

Drew,
The test results that you have provided high-light the fact that the person that discharged the gun prior to the barrel failure was negligent; in that he/she failed recognise the potential risks involved when ever a weak/blooper discharge is experienced.
it should be standard practice for all participants in shooting sports, that when ever a weak discharge/blooper occurs the shooter must check to ensure that that the barrel is clear of obstructions prior to reloading and firing another shot."
The test results indicate that in the failure under review that this safety precaution was not followed.
Collectively we need to stress the importance of following the safety check described above in particular with every new entrant to shooting sports and for that matter some experienced sportsmen.

Drew,

Thanks for taking the time and going to the expense of having this testing done! The information revealed is invaluable to those of us who are fascinated with damascus barrels.

Thank you Doc Drew for your time, efforts and investment. Your investigation along with that or Sherman Bell and Tom Armbrust have gone a long way to dispel the myths surrounding the dangers of the use of firearms with Damascus barrels so long as they are in good condition and they are used with the loads they were designed for. Perhaps this will encourage manufacture's to start listing actual chamber pressures on their products.

Thanks guys, but there is ALOT more work to do. I think Adam's intellectual curiosity has been stirred, and hope he, Eldon and Steve will continue what has been started. We're already way past my cognitive capacity...and checking account
We should all be thankful to the guy who allowed the analysis of his blown barrel, despite the risk of criticism. Over the last 5 years or so there have been lots of posts on public forums about blown barrels, but no one seemed interested in actually finding out the cause. And many thanks again to all those who graciously provided knowledge or barrels, without which there would have been no NDT or tensile strength testing.

Steve: please think about visiting Paradise before the 2015 Las Vegas show and spending some time with Adam at METL!

Drew,

I will definitely be continuing work and research on damascus barrels. I am very interested in communicating with Adam and would like to come down for a visit. At the very least he should have my email address, in case there is any information that he may need to know about the forging process. Please feel free to provide my address to him.

I remain surprised at the very low carbon content of the tested barrel section. The chemical analysis essentially states that the two components are two different grades of wrought iron. I based my assumptions on the carbon content of the "steel" component of damascus barrels, largely on the writings of Greener. But also from writings in the French language, where the barrel components are referred to as acier (steel) and fer (iron). I remain reluctant to make an industry wide statement about the materials used, based on this one test result. I will look into having chemical analysis done on other barrels, to have more results to compare.

Thought I'd apply Barlow's formula to the subject barrels



The chambers are 2 5/8" and the wall thickness at the end of the chamber was .119". Estimating the OD is difficult so did ID + wall thickness X 2. This does not include the brazed flats which obviously provide significant additional metal/strength to the breech, but the barrel blew out laterally.

SO Barlow's formula P = 2 x S x t / D
P=Bursting pressure in psi.
S=Tensile strength of material in tube wall.
t=Wall thickness in inches.
D=Outside diameter in inches.

Burst pressure = 2 x 54000 x .119" divided by 1.053"

And the number is only 12,205 psi?!?! What am I doing wrong?

Chuck's calculation on p. 4

My SWAG is well in excess of 15K psi. Say 25,000 psi.

1) I base this on my estimation of the strength of the Damascus being around 60,000 psi ultimate, providing for mild steel being around 64,000 psi, and ductile iron being around 60,000 psi and some conservatism.

2) I used .100 as the Min Wall

3) A hoop calculation of a .798 I.D. chamber and .100 wall with a 60,000 psi strength is around 15,000 psi.

I appreciate that you're looking where the facts seem to take you. On the surface of it, there would not seem to be a requirement for a very large pressure spike to cause this particular failure.

Maybe the lab folks would confirm your calculation and comment on possible adjustments to the formula because of the rapid rate of the pressure change. Maybe they'd comment on how the tensile test sample failures compared to barrel blowout.

You've mentioned recommending loads as intended for the original gun. Probably a good guideline and possibly easy to run questionable pressures without obstructions. Really looking forward to the article, nice job.

Drew;
My knowledge of this is somewhat limited, but my understanding is that Barlow's formula is for high Pressure tubing under a constant load. Firing a shotgun does not produce that constant load, but only very briefly reaches its peak pressure. It is my understanding it takes a considerably higher pressure to bulge or burst a barrel than that indicated by Barlow's formula. This is what I was hoping some of our engineering Friends would chime in on, as to just what formula is most applicable for this purpose.

As does Miller, I'd very much like to hear from someone who understands this stuff.

I did get some help from Adam at METL who is a metallurgical engineer and not a mechanical engineer.

Barlow's refers to a pipe capped at both ends with a static pressure. The barrels aren't designed to be pressure vessels as one end is open. This is why an obstruction could cause a rupture at a pressure below proof pressure. 12,205 psi may be the right value for stress the barrel can sustain if it were capped at both ends.

Drew;
I think that 12,205 psi would be the static pressure it would contain if capped at both ends & if it were of the uniform diameter at which you calculated it. Obviously if it were capped at both ends & a static pressure applied it could be no higher than the weakest point in the barrel could contain. Since in firing a shotgun we are dealing with a pressure curve rather than a uniform static pressure the entire barrel does not have to be able to contain the Max pressure. The forward, thinner portion can be burst at a pressure which is lower than the max chamber pressure. Indeed under controlled test conditions barrels have been fitted with the normal pressure sensor at the 1" mark & obstructed with the barrel being burst at the obstruction without recording any increase of pressure in the chamber.

It might be noted though that pressure is recorded in a gun barrel even though one end is not capped, and chances are the part of the tube where the sensor is located is subject to that force however brief. Maybe for an obstruction that causes a burst, enough pressure formed to cause the burst even if a lower pressure were recorded at a different location.

If you run Barlow's Formula for a standard .729" bore at a forward location having an .030" wall you get a burst point of 3,645PSI with that same 54,000 PSI steel. When the shot hits an obstruction a localized pressure builds up, at that point. If that local pressure exceeds the yield strength of the steel a bulge will occur, if it exceeds the ultimate strength a burst occurs. When the barrel bursts, the gasses are fred so pressure falls rapidly, thus never reach the pressure recorded at the breech upon firing. The load in the bore of course makes it a Sealed Chamber, But the load is Movable & Not totally fixed, thus not a True Closed Cell pressure.

As suggested by others, reference should be made to volume 3 of the Modern Shotgun,"The gun and cartridge", chapter 16 Bursts!.In this chapter Burrard reviews steel strength, yield versus ultimate strength,together with comments on performance applicable to Damascus. Formulae relating to barrel design/strength are also given. The effects of wave pressure caused by barrel obstructions are reviewed in detail. Perhaps a person interested in this issue with a degree in mathematics/physics could comment on the impact of wave pressure on the barrel failure as seen in the samples under review.

Roy;
I presume this is probably a lot of the same mat'l as found in Burrard's The Modern Shotgun. He does in this work show a barrel which received three bulges from one shot. The obstruction was not quite severe enough to cause a burst, but as it moved down the barrel the Wave pressure bounced back to the breech, forward again until it caugth back up, creating the second bulge & eventually the third. Each successive bulge was smaller than the previous one.
One often hears how "OutDated" Burrard's work is, but after having studied it for many years I am of the conclusion that except for the substitution of Plastic for paper & felt, not much has truly changed.

2-piper
First thank you. I have correct, my post it should have read, The Modern Shot Gun. Yet another of my Seniors moments.
In my opinion Burrard's research on bursts has not been surpassed. Today it can be enhanced by adopting current methods for evaluating materials chemistry, stress measurement and none destructive test methods,

I've got a mechanical engineer on this, but here are some formula for a thick wall (wall thickness greater than 1/10 - 1/20 ID) pressure vessel (again a closed system under static pressure)

Our subject Remington 1894 barrel:
Wall thickness at the end of the chamber was .119"
ID at the end of the chamber = .815”
OD = ID + wall thickness X 2 = 1.053”. This does not include the brazed flats which obviously provide significant additional metal/strength to the breech, but the barrel blew out laterally.

Barlow's formula P = 2 x S x t / D
P=Bursting pressure in psi.
S=Tensile strength of material in tube wall.
t=Wall thickness in inches.
D=Outside diameter in inches.

Burst pressure = 2 x 54000 x .119" divided by 1.053" = 12,205 psi

Burrard quotes Alger Burst Formula
Burst pressure = Ultimate tensile strength x 3(OD – ID) / OD + 2xID

54000 x 3(1.053 - .815) / 1.053 + 2 x .815 = 14,370 psi

Lame Formula
Burst pressure psi = Ultimate Tensile strength x (OD squared – ID squared) / OD squared + ID squared

54000 x .446 / 1.774 = 13,576 psi


Short version of wave pressure per Burrard is that it can be more than 200% of shell pressure depending on the load, location, and degree of obstruction

Well my gen-u-wine mechanical engineer buddy helped enormously - "It's kind of a complex problem" but Barlow's is close enough for non-deep thinkin' victims of a public education in the great state of Missouri

My increasingly squishy brain has been contemplating these numbers with some concern but it should be noted that Sherman Bell's sequentially increasing load experiment did not blow out the chamber of a Parker VH Damascus until almost 30,000 psi - about 2 1/2 times Barlow's burst pressure. 'Zircon's' unpublished metallurgical examination DID show low cycle fatigue.
Our examination of the obstruction burst (a single high pressure event) did NOT show low cycle fatigue however.

We know the ejecta is moving before maximal pressure is reached in the absence of an obstruction