If a set of Damascus barrels very recently passed London proof with less than .025 minimum wall thickness in one of the barrels, would you be comfortable shooting RST or equivalent light loads in it?

Would you be uncomfortable buying the gun, though in proof, because of concern with ever being able to re-sell it with BWT less than .025?

No, I wouldn't be uncomfortable shooting the gun with appropriate loads, especially if the thin spots are well forward. But I would always be nervous about denting it. Be hard to properly repair. And yes, it probably will be more difficult to sell if the buyer is given full disclosure.

If the seller is unable to tell you exactly WHERE that .025" was measured, I would pass Rich.
If it's the distal 1/3, lots of light weight 12s and small bores left the makers' shop that way.

No concerns other than thin barrels do dent easily. They just passed proof so what more "proff" of fitness to shoot could you get. On a personal note I want those thin areas far away from my face and hands. The last ten inches is fine.

As to resale issues you can't sell a Damascus barreled gun to anyone who does not understand them. A educated buyer, who knows where a barrel is thin will make a judgement call if he wants to buy the gun. You just give them the facts, barrels this thick and passed proof at this time. A few won't buy but many would.

I agree with Joe and John. Depends where it is thin, how thin it is and for me, price point.

No, I wouldn't be concerned, I shot RST's out of a damascus 10 guage with 21 thou a few inches back from the muzzle. However, there was something like 135 thou at the forcing cones and plenty of thickness through the 2/3 of the barrels from the breech.

When barrel wall thickness is given, where is it most commonly taken on the barrel? I know that near he breech is most important, but if the thickness is stated, where is the measurement typically taken?
Karl

Karl, my understanding is that minimum barrel thickness is measured at wherever the thickness is least. That is, various measurements until the minimum is located. That would, of course normally be in the forward 9 inches or so closest to the muzzle...Geo

I shoot a Manufrance Ideal with MBT of .021 but its at the end of the left barrel and I don't worry about it.

George,
Thanks for your response. I've often wondered when gun dealers will state the MWT of the barrel, where it is most often or traditionally measured.
I just picked up a pre-war English gun at .036 and was curious.
Karl

If I remember correctly, the minimum wall thickness to pass London proof was 0.020 for many years. A few years ago, (maybe 5?) I started seeing guns coming through the Holt's auction with recent proofs that were under 20 thou. Not sure what changed that, or when. If a damascus gun had 0.025 tubes, I'd be pretty confident in it (with proper loads, of course).

There is no such thing as minimum wall thickness to pass proof and there never has been. Ever.
They either pass proof or not. Wall thickness is immaterial and not even measured.

Thanks very much for all the good comments. Much appreciated.

popular wisdom suggests that one should not shoot a fluid steel barreled gun with a barrel wall thickness of less than .030 inches...so why take the risk, of shooting a damascus barreled gun with such thin barrels? makes no sense to me...when there are plenty of fine heavier barreled damascus guns that are safe and fun shooters with black powder loads?

“Popular wisdom” what is your reputable source for this fact?

While some may throw out a number, it is a throw not necessarily a fact based on testing. This why there is a proof house to provide some reliable basis for judgement.

While 0.025 is on the low end, as others have already noted it depends on where. My father and I have put more than a thousand shells (custom low pressure sub 6k) through a pair of Damascus barrels barrels which are below 0.030.

Blue Grouse is totally correct: MWT's have never figured in the proof test. The Proof House RECOMMENDED a MWT of 20 thou until steel loads became common and has now increased it to closer to 30 thou.
Ed Good: there are relatively few damascus barrels out there that measure in excess of 0.025" MWT's. They may have started life with nice thick walls but old corrosive primers, rebrowning etc have reduced most to high 20's at best, many are in the low 20's.
Karl Graebner: when measuring MWT's, you slide the barrel up and down the gauge looking for the minimum reading, whether it is just in front of the choke or just in front of the chamber.
I exaggerate because it is very difficult with a traditional MWT gauge to measure up close to the muzzle and most MWT gauges are about 15" long so unless one suspects something scary, one stops at that point from the muzzle.
There is no particular place that one states the MWT for, it is any spot on the barrel. If it was in a 'bad' place then I would state that in describing the gun.
As a point of interest, most barrels made in the UK from the last 1/4 of C19th to present do not taper from muzzle to breach.
They are often described at 'Eiffel Tower' profile, ie. they taper to around the mid point then the MWT's get slightly greater toward the muzzle. I understand that gives better dynamics to the barrel, reducing overall weight but increasing the strength of the tube near its end to accommodate the choke and risk of impact damage.
This means that if the bores are properly parallel (often not the case with guns that have been 'creatively' bored [!]) the thinnest MWT's measurement will be in the mid section of the barrels. On post 1880 guns, I find this is usually the case.

Toby,
Great explaination, thank you for posting. Having purchased my first English double after owning several other SxS's had led to my curiosity.
Karl

I believe it would be unwise to purchase a vintage double, of any maker, without knowing, or being able to measure accurately oneself the end of chamber, forcing cone, 9” from breech, 9” from muzzle, and exactly where the MWT is found.
And breech to muzzle bore measurement looking for a bulge not apparent on external examination.
Bad things happen to good guns after 100 years or so.
https://docs.google.com/document/d/1ZIo0y746UsSRZIgRuuxwAbZjSBHitO_EanvwLYc-kGA/edit

Bro. Toby's "Eiffel Tower" profile is well said and fits my experience with U.S. makers also

Standard dimensions of each barrel tested as part of the 1891 Birmingham Proof House Report from "The Field" March 7, 1891 Vol 77:325
http://books.google.com/books?id=inQCAAAAYAAJ&pg=PA9
NOTE: these dimensions do NOT represent MWT, but show the "Eiffel Tower" profile. The chambers are not cut nor do the barrels have choke constriction



Mark Twain
“It is better to be careful 100 times than to get killed (or kill a bystander with a chunk of shrapnel) once.”

"Experts on Guns and Shooting", George Teasdale Teasdale-Buckell, 1900
http://books.google.com/books?id=4xRmHkr7Lp8C&pg=PA526&source

My personal policy is MWT has to at or north of .030. That eliminates some nice guns from my consideration, but my fingers appreciate knowing the barrels have extra meat in them. Again, just my personal policy.

I had an untouched Damascus CH Parker 16 and Crossed Chisels measured it at .018 and .022. Both thin spots were about 6 inches from the barrel ends. The barrels had not been honed, they were just struck that thin. Far as I know it is still knocking birds down with the appropriate ammo.

That Eiffel Tower profile was named hundreds of years ago .........."swamped". Some "schools" of muzzleloading longrifle barrels were struck that way over here 250 years go. It not only strengthens the muzzle area against dings but it also helps the handling characteristics. And, on a KY/PA longrifle which may have a barrel well over 40" long, it is beautiful. IMMostHO.

SRH

toby: based upon my observations, it seems reasonable to state that typical english made field guns would have thinner barrel walls than typical american made field guns...and, the sin of barrel honing has only recently begun to be practiced in this country...

Gee, that's very interesting Ed. Thanks for offering even more proof that you don't know what the hell you're talking about. You ought to stick to things you are good at... like torch coloring guns, Trolling, and posting anti-2nd Amendment drivel.

Recall the sad story Ballistix999 told us about the 20 gauge Clarke he restored and which passed proof. After 6 rounds, the left barrel split. Fortunately no one was hurt, but that was that.
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=237716&page=1

I'm guessing the "repaired" bulge might have had something to do with that failure.

Anyone know where the bulge/crack was located? Near the chamber? Near the muzzle?

It was just in front of the chamber area. About where the forcing cone would transition to barrel bore. On page three of the original thread.

This might be controversial, but I don't mind even 17-18 thou in a 12-gauge that is otherwise in very good condition. With proper low-pressure loads I would shoot it with confidence. On sub-gauge guns I take a markedly-different tack. Sub-gauge guns (especially 20s and smaller) seem to operate at much higher pressures and I'd want a minimum of probably 25-thousands (and would prefer 30).

Remember "Low Pressure" loads are of benefit "ONLY" for lowering the pressure in the chamber area, no farther than about 4" from the breechface. "IF" the same shot load is propelled to the same velocity, then the pressures forward of that will actually be Higher with the low pressure load. If the MWT is down the barrel
where it should be one is not doing it a favor my shooting Low Pressure loads unless that low pressure is obtained by the use of a lighter shot charge &/or a lower velocity, which can still use a fast burning powder. Slow powders will slightly raise the pressures beyond that approximate 4" mark.

Would everyone who feels comfortable shooting guns with barrel’s MWT at 17-18 thou let their kids or grandkids shoot it? The gun might be in proof, but.....

I agree with tut (on page 2), if I set minimum wall thickness at an arbitrary .030 near the muzzle there are many in my safe that should go to the junk pile instead of the field. I have a number of Parkers, for instance, that can't pass that test and are definitely untouched. This discussion will never be settled--it is strictly up to the individual and in a sense neither side is wrong. Where I do get real skittish is in the chamber area and the next couple inches. Even there though I often drop below the commonly accepted dimensions. My gun, my fingers.

Not trying to be a smartalec but your logic is a little bit off. All else being equal, wall thickness etc. the smaller diameter tube will withstand a greater pressure. Not an insignificant difference either.

Years ago a story was told of a man who had a Model 12 trap gun that was so worn there was a pinhole at the end of the barrel. When he shot, a little puff of smoke came up out of the hole. Everyone figured there couldn't be any choke left in that barrel, but he believed in the gun and he broke targets with it. Finally when the gun was in to be repaired for something else, the gun smith welded up the little hole. When the gun was given back to the man, he said he's kind of missed the little puff of smoke.

Thank you Blue Grouse & Toby Barclay for straightening out misinformation posted early on in this thread regarding MWT and Proof House.

I owned a gun a couple of years ago that had just passed London Proof with a MWT of .018.

Miller, I think I may be missing something here. Seems to me what you wrote can be interpreted as saying that pressures on low pressure loads INCREASE after they leave the chamber. I've never seen a pressure curve that goes in any direction other than down after leaving the chamber. I think you're trying to say that pressures on higher pressure loads using fast burning powders drop off faster than they do on lower pressure loads, especially those that use slower burning powders. But whether the lower pressure load's pressure is higher than a higher pressure load at any specific point on the curve depends on the specific loads and how much difference there is between them to start with. I think the only generalization that can be made is that lower pressure loads often show a slower loss of pressure than do higher pressure loads.

1cdog - In one of our previous discussions it was reported that the Birmingham Proof House would notify the owner if the gun had a wall thickness less than .020". Was that done with your gun? Did you receive a copy of the Proof House certificate? Could you please post an image if so? Thanks.

Larry;
Quite possibly I didn't word my statement perfectly,though I thought every one could understand what I was saying. Yes it is totally true that pressures falls for the rest of the barrel's length once the max chamber pressure has peaked. "However" f the same ballistics are kept those pressure curves will cross in the area from about the end of the chamber to around 4" from the breech.

From that point forward the "Low"pressure load will have a higher pressure than will the "High" pressure load. This was intended as a Reminder, note the word "Remember".

Pictures of these pressure curves have been posted Here on This forum many many times & they have been thoroughly discussed. I truly felt like anyone but an "Idiot" would understand what I was saying, You "DID" understand didn't you.
Yea!! I though so you just proved beyond all doubt that you are qualified.

Us non-deep thinkin' types do better with pictures

Sherman Bell’s pressure testing published in The Double Gun Journal Summer 2002 “Finding Out for Myself, Part VI, Smokeless vs Black”, p.19, and summarized in Volume 17: Issue 4, Winter 2006, p. 39
1 1/4 oz. 3 3/4 dram (102 gr.) GOEX FFFg Black Powder at 1240 fps and the equivalent load of Blue Dot. That is a boomer load few of us are likely to be using in a vintage double

................1 inch........6 inches.......12 inches
GOEX.........5900 psi......4100...........2100
Blue Dot.....6000..........4300...........2300

At 6" modern "non-progressive burning" powders are about 1/2 of Blue Dot's and GOEX pressures, and at 12" well below 2000 psi. Alliant data for 1 1/8 @ 1200fps

Alliant e3 - 17.2 grains = 10,950 peak psi
Red Dot - 18.3 gr = 10,300 psi
Green Dot - 21 gr = 8,900 psi
(Infallible) Unique - 22 grains = 8900 psi

we talk a lot about minimum barrel wall thickness, but what we really should be talking about is barrel wall thickness in front of the chambers, where the maximum pressure typically occurs...my gunsmith, old ed, recommends not firing a 2 3/4" chambered 12 gauge gun with less than .090 thousands in front of the chambers...what say you?

Ed, Am I reading the charts wrong or are you? They all seem to show the maximum pressure well within the chamber, not in front of it.

The chart seems to show there is no difference after 2" which is within the chamber.

"Chamber pressure" is 1" from the breech

Wallace H. Coxe, in “Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics” published by E.I. du Pont de Nemours & Co., 1927, “Measurement of Pressures”
The common method of taking pressures in small arms in this country is known as the Radial Pressure system. A housing is built around the barrel, and a hole drilled through the housing and barrel into the chamber at a distance of 1 inch from the breech and at right angles to the axis of the bore. The hole is then bushed and drilled to a uniform diameter of 0.2250 inch. Then a piston is made the length of the piston hole and 0.2250 inch in diameter. Next the piston hole is lapped to permit the piston to fit snugly without either sticking or getting out of alignment.
In firing the gauge, the piston is inserted and seated, then a lead crusher cylinder is placed on the head of the piston and held firmly in place by a screw and anvil attachment built into the housing. When the cartridge is fired, a portion of the same gas pressure that pushes the bullet through the barrel drives the piston against the lead cylinder and compresses it.
The length of the lead crusher cylinder after compression is naturally less than before the shot was fired and the difference between the original length and the length after compression therefore represents the amount of pressure which has acted upon the lead. Thee exact pressure is read from a table giving a pressure reading for every remaining length reading and commonly called a Tarage Table.
Pressures that are determined at ballistic laboratories are merely relative values and are not absolute values.

Modern piezo transducers can be placed every inch if so desired

I don't believe London proof has existed for some time. And Birmingham proof has been increased considerably. Two proof rounds are fired in each barrel.
Dig had an article in DGJ that pointed out a model of Cogswell and Harrison was gathering a reputation for failing reproof, the article had photos of an old gun with a cracked frame.
I suspect that many of these same guns would be just fine if used with the loads they were designed for, but, can offer no proof.
The only double guns I ever had that had .030 of muzzle wall out to the 9" from breech measurement were Darnes. My Italian guns left the factory at about .025 in that area of measure.
I'm not interested in doubles at .020 or less, in the same area. I use my guns.



Best,
Ted

Ted: I couldn't find the previous thread discussing the inexplicable failures at the Birmingham Proof House, but this was clarified to mean ONE round that develops the desired pressures at both 1" and 6.38"

2006 British Rules of Proof
http://www.gunproof.com/Proof_Memoranda/RULESOFP.PDF
Part IV, “The Proof Load”, Number 27, Part A
Calls for a load of 30% over mean service pressure at a point 17mm or 25mm (about 1”), and at a point 162mm (6.38”) from the breech face a load of 30% over mean service pressure (at that point as determined by the Proof House).

"Mean Service Pressure" is probably 650 bars (9,427 psi) or maybe it is “Maximal Average (Service) Pressure” 740 BAR = 10,733 PSI.
“Mean Proof Pressure” is 930 BAR = 13,488 PSI, or maybe 960 bar = 13,924 psi.
9,427 x 1.3 = 12,255
10,733 x 1.3 = 13,953?

What the pressure is suppose to be at 6" is a secret, as is the powder in the proof load, and I've given up

My point was (obviously lost or not conveyed well enough) was that guns pass proof with low MWT.

Not that I recommend using them that low.

For the record I use my guns too. Year round........

Cheers!

That is indeed what Drew's graph shows: No discernible crossing point. The often-cited Dupont graph (from 1933) shows a crossing point at about 2 1/2", where the lower pressure loads overtake the higher pressure loads. That same graph shows that by the time they reach a distance of 7", there's a spread of about 500 psi between high and low. And by the time they reach 10", there's no significant difference.

so, rather than quibble about exactly where maximum pressure is, how much barrel wall do youse guys like in front of the chambers, or do you care? i have seen enough guns with barrel wall bulges in front of chambers to consider barrel wall thickness in front of chambers to be an even more important safety issue than minimum barrel wall thickness...

Well Larry, the point is "IF" the same ballistics are met, if the max pressure is lowered it "Will" be made up somewhere else. The laws of physics have not been changed. As max pressure is reached inside the chamber the "Make-Up" occurs over the rest of the barrel's length, so the difference in pressure is much slighter than is the Max.

Bottom line is though that shooting a "Low Pressure" (IE low max chamber pressure) load ii no way makes t Easier on the barrel at a point some 18" down the bore. The pressure there will in fact be very sightly higher, though mostly insignificant. Just don't be fooled into thinking that shooting low pressure loads are of benefit anywhere other than in the chamber itself for they are not.

With all due respect to Drew, the problem is the pics he posted are simply not detailed enough to show that slight cross over. It is simply impossible to get the same ballistics & have that much difference in max pressure & it not be compensated for else where.

I high resolution scanned this from my copy of the 1927 "Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics" by Wallace H Coxe.
It doesn't tell us everything, but probably tells us something about the pressure curves of the powders
Ballistite - Dense Smokeless
Schultze and DuPont both Bulk Smokeless
FFFg BP
DuPont Oval the first "Progressive Burning" Smokeless

What you say is true, Miller. But we know for a fact that we can have loads that differ by a few thousand psi PEAK pressure. It'd be interesting to chart loads with those very significant differences vs those that only differ by 1,000 psi or so peak pressure. But what the old Dupont charts show--like Drew's, and like the 1933 chart I'm looking at--is that by the time you reach 6" from the breech, the difference is already insignificant--in the range of 500 psi.

So it seems to me that it depends on where you're worried about pressure, because from 6" or so on, the curves merge together even closer. As far as pressure is concerned, beyond that point there's no reason to concern yourself at all--at least as far as the difference between loads is concerned. If your barrel is going to fail due to pressure at that traditional 9" measuring point, I doubt that the lowest pressure load at about 3,600 psi would save it from happening with the highest pressure one at 4,000.

Larry;
Agreed; read this line from my last post "The pressure there will in fact be very sightly higher, though mostly insignificant". This is what I have been saying for ages. People though still keep saying I have barrels which are thin in the forward end, therefore I am going to shoot "Low Pressure" loads to protect them. They are simply like an ostrich with their heads stuck in the sand. True the difference is very slight, but whatever difference there is, it is in the opposite direction of their stated goal. Nuff said, you either have it by now or you'r one of the Ostriches.

Another pressure curve to demonstrate Miller's point
“Powder Pressures At Different Parts of the Gunbarrel”, 1895
https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA32&dq

The choice of 32 grains of Ballistite is confusing, as 25.5 grains is the published load for a 3 Dram equivalent.
According to https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA7
this is the Dram Equivalent for the grains listed for the Nitro Powders:
Ballistite 32 gr. = 3 3/4 Dr Eq.
Walsrode 34 gr. = 3 1/8 Dr Eq.
Cannonite 38 gr. = 3 1/8 Dr Eq.
Schultze 42 gr. = 3 Dr. Eq.



All 4 curves meet at 6" but at 12" the pressure for Dense Ballisite is 1600 psi by Burrard's conversion; Bulk "Schultze" 1900 psi. The difference continues out to 24". Of course no "progressive burning" powder was available in 1895.