doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Barrel ring bulge revisited

The recent resurrection of Tony�s thread re the 20 ga Clarke got me wondering about bulges again. I�ve read (ie, Shotgun Technicana) that any dent must be repaired because a dent is a form of an obstruction and therefore dangerous. On the other hand, I�ve read that many barrels with bulged barrels are safe to shoot, depending on whether the bulge is in a low or high pressure region. This brings me to my question that I�m hoping an experienced gunsmith or metallurgist will try to answer. What to do with bulges close to the breech? Close to the breech is a high pressure area, a likely unsafe area for a bulge. I�m assuming a bulged barrel in this area is unsafe to shoot, but is a bulge in this area amenable to repair? It seems to me that once the metal is actually stretched after reaching its elastic limit, it�s molecular structure is forever changed. I�ve read on this forum that hammering down a bulge actually hardens the metal. Is the entire bulged area now competent since it is hardened after being hammered down? What about being more brittle since being hardened? Are theire faults in the hammered areas that would be prone to rupture or is the area now sound and 100% competent? How would one know for sure after repairing a bulge in a high pressure area if the repair is sound or prone to rupture? I�m guessing electron microscopy looking for voids would be about the only way to tell for sure, but I�m not a metallurgist. I�d be interested in educated opinions. I have a friend who has a gun with this very problem, a ring bulge close to the forcing cone.

Bro. Buzz: I only play a metallurgist on the internet, but have been told by several smiths that ANY defect near the chamber/forcing cones makes the barrels unusable and unrepairable.

Then again

Experts on Guns and Shooting, George Teasdale Teasdale-Buckell, 1900
http://books.google.com/books?id=4xRmHkr7Lp8C&pg=PA373&dq
On the subject of steel v. Damascus, Mr Stephen Grant is very clear, and much prefers Damascus for hard working guns. He related an anecdote of one of his patrons, whose keeper stupidly put a 12-bore cartridge into his master�s gun without knowing that he had previously inserted a 20-case, which had stuffed up the barrel. Fortunately, no burst occurred, but a big bulge, which, however, Mr Grant hammered down, and the gun is now as good as ever.

The Clark had a bulge close to the chamber. It was worked down and passed proof. Then failed after six shells. So I would not even try to repair any barrel with a bulge within the first 18". Eyes and fingers are in that area and don't respond well to barrel failures.

You have studied metallurgy in Damascus, for sure there Drew. I�ve seen the electron micrographs to prove it. I�ve had gunsmiths tell me �no go� too and others who have said they possibly can make the repair. It�s very confusing and there is really no literature regarding what may be repairable and what isn�t. It�s sort of an alchemy sort of thing. The Clarke gun failed, even after British proof, but that�s no guarantee all will fail nor even a majority. I think it may well depend on multiple parameters including how bad the bulge is, quality of the metal material, thickness of the walls at the bulge, as well as others. The Clarke was a very old gun so the steel may have been archaic and not as good as more modern steels, but that�s only a guess. It would be nice if we had some sort of cookbook to go by defining what likely could be repaired and what can�t. There�s nothing out there defining that which I can find.

If the barrels were something like Siemens-Martin steel, Buturlin cited studies conducted at TOZ (Tula Arms Plant) listing Russian Siemens-Martin tensile strength as 85,300 � 92,400 psi; modern AISI 1040 gun barrel steel is 95,000-100,000.

I believe the concern on the part of gunsmiths is liability should something like this happen



Asymmetric obstructional 'ring bulge' related to the addition thickness of the brazed barrel flats and support of the right barrel



For a right hander, that chunk of chamber would go right past the left eye

And neither magnetic particle imaging nor radiography could show microscopic voids in the repaired bulge barrel wall

Obstructional burst just past the forcing cone.



The chunk hit the shooters forearm, but he only required sutures for repair





You might ask your friend to take a look

Not shooting guns with thin barrels, ring bulges, etc. is called risk management. Why anyone would is beyond me. Shooter beware.

popular wisdom says not to shoot guns with bulged barrels and not to attempt to repair barrels with bulges...

From what I�ve read all bulges are not the same. For example, it is perfectly safe to shoot many guns with bulged barrels IF the bulge is in a low pressure area, such as close to the muzzle. I agree, you are rolling the dice shooting guns with a bulge close to the breech and in high pressure areas. That�s the issue here, trying to define and identify those situations where a gun with a bulge near the breech may be safe from those that are not and which ones could be repaired. Or, should ALL guns with bulges close to the breech now render a shotgun barrel junk and then off to the junk pile?

There is no inherent difference in a dent and a bulge, except for the extent of it. One is pushed in, the other out. Metal is stretched in both instances. I have repaired both. Dents are much easier, because they're usually much smaller than ring bulges. There is much greater chance for a split to be present with a ring bulge, IMO. I cannot explain what actually occurs when you peen a dent out with repetitive light hammer pecks, not being an engineer or well versed in metallurgy, but it appears the metal "flows" back into nearly the original dimensional state. The only bulge I ever removed was a ring bulge that was about 10" from the muzzle on the right barrel of a 30" set. I knew I couldn't get it all, because it extended all the way around and was, obviously, under the ribs as well. After several sessions of peening, the top rib popped loose. This necessitated the complete removal of top and bottom ribs, and facilitated a more complete removal of the rest of the bulge. However, it was then found to have a split in the section of the bulge between the barrels, which was tig welded.

Bulges are bad news and, IMO, must be evaluated individually. The bulge I removed was what I would call a severe ring bulge, with much metal displacement ............thus, the split. I would never consider shooting, or repairing, one anywhere near the breech, and it would have to be a very "mild" one even then.

SRH

Thanks Stan. I do not think we should forget that in Shotgun Technicana they explicitly say dents are obstructions and should always be repaired before firing the gun no matter how minor the dent. . This is opposed to bulges which are not obstructions.

One other consideration we seldom think about buzz, is that even fluid steel is not a perfectly pure and homogeneous product. The chemistry and metallurgical qualities can and do vary between heats and even within the same heat. There are varying amounts of impurities and inclusions such as rolled-in scale. So the strength of two seemingly identical dents or bulges in exactly the same place and with identical wall thickness may not react the same to equal pressures. If you've ever drilled, tapped, or machined a piece of steel and suddenly hit a spot that took off the cutting edge or broke the tap, you know that you've encountered one of these hidden defects. This is why they proof test the barrels of brand new guns, either internally by the manufacturer, or in government proof houses.

A ring bulge always stretches the meta, I personally do not believe that all dents do. I fact I think a great number do not.
I have mentioned several times abut the "Crack" in a parts Twist barrel H grade Lefever I acquired had. One side of the crack was inward & the other outward. My "theory" is the barrel was dented & made the crack, then subsequently fired & the unsupported side raised. I placed by dent plug under the crack, raised the inward side hammered down the outward side. Every thing fit so perfect-fully after repair one has too look"Extremely Close" to find where it is. NO metal appeared stretched on either side. This brrel was subsequently fired with factory loads of 3 1/4-1 1/8 & 3 3/4-1 1/4 loads as well as a hand load off 1 3/8 oz, DE unknown. It was fired remotely via ye ole Firestone proof facility. Nn of these lads opened the crack in the slightest, nor did any Soot appear at the spot.

I have repaired one bulge. This one was on an Ithaca semi-auto & was just behind the choke. It was caused y a known obstruction. I removed the vent rib & then removed the "Cutter" from a pie cutter (Not a little tubing cutter) & just rolled it back down. Last I heard from it was still going strong.

I am not a metallurgist either but one machine shop I worked in I made a lot of test specimens for the "Met Lab". This much I did learn from taking with those wh did the testing. When pulling a tensile specimen when the Elastic limit is reached the metal suddenly stretches. Upon release of the tension it will not "Spring back" to its original state. how ever as the test continues to its ultimate where the specimen is broken more pull force has to be applied than what "stretched" it beyond it elastic limit before further elongation takes place.
This says to me that the just stretched steel is now stronger than it was just prior to stretching.

Somewhat surprised Rocketman has not weighed in on this, this is in his field of expertise.

Just a reminder gentlemen. All gun barrel steels are not equal; in neither yield nor tensile strength. One barrel might tolerate bulge repair; another may not.

Tensile Strength
Pattern Welded steel � 55,000 psi
�Cold Rolled� Decarbonized Steel & AISI 1018 Low Carbon (Mild) Steel � 65,000 psi
1890s to c. 1920s fluid steel (Krupp, Siemens-Martin, Cockerill) � 85,000 to 90,000 psi
AISI 4140 Chrome-Molybdenum Steel, Winchester Nickel Steel, Marlin �Special Smokeless Steel�, Remington Ordnance Steel, Bohler �Blitz� - 95,000 to 110,000 psi
Winchester Proof Steel (Chrome Moly 4340 or 4130) developed for the Model 21 and introduced in 1931 - 120,000 psi
Bohler �Antinit� Rostfrei Laufstahl chrome-molybdenum-vanadium � 140,000 psi

And remember: Tensile strength is only a part of the equation for estimating bursting pressure. If the barrel is made of steel with a 60,000 psi tensile strength, that does NOT mean that it will withstand a shell with a 10,000 psi by a factor of 6.
Barlow's Bursting 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.
Barlow�s refers to a thick wall pressure vessel (wall thickness greater than 1/10 � 1/20 ID); ie. a pipe capped at both ends with a static pressure.
Shotgun barrels are not designed to be pressure vessels as one end is open.

https://docs.google.com/document/d/1dnRLZgcuHfx7uFOHvHCUGnGFiLiset-DTTEK8OtPYVA/edit

I would like to ask a question about barrel bursts due to barrel bulges. May I assume that bursts of barrels, even with more slight ring bulges, say at about mid barrel, are due to the weakness of the metal at that point? That it is the effect of pressure and weakened metal?

I don't want this to sound like a trick question I am interested in this and would like to understand.

If pressure and weakened metal are the cause of the burst how is an equally extended dent different? Directional?

I am interested because at a point in the past I sent a Fox away to have dents removed. After it was returned to me I realized it had a bulge, so slight I have to hold it to a light to see and even doing this I can't feel it. It is a slight ring bulge.

I am trying to determine if I should send it for removel or leave it as it is?

I have heard the term work hardened and know that would apply to a repair, but I have also heard that ring bulged metal is work hardened by its creation?

I already have invested all I want to put into this gun but $50 or $60 to have a nearly invisible dent removed is not that much if it makes the gun safe to use, but does it?

Thanks for all interested, helpful replies.

Most barrel bursts are due to an obstruction in the bore. A bulge may also be caused by an obstruction that is not enough to actually burst the barrel, such as a light plug of snow in the bore.

While dents and bulges are both a displacement of metal, a dent may be worse than a bulge of similar displacement because it partially obstructs the bore. Also, a dent may be a shallow depression, or it may have been caused by a sharp object that leaves a more stress damaged area.

If the bulge you describe on your Fox is so minor that you have to hold the barrels up to light to even see it, and you can't really feel it, then I wouldn't lose any sleep over it. In fact, attempting to hammer it down could pop a rib loose.

In fact, something that minor might be a short section of rivelling. Rivelling is a weird phenomena we sometimes see that typically occurs in areas where the barrel wall thickness is thinner. It may occur in a very short section, or run for half the length of the barrel. It can look like one or more small ring bulges, or a series of ripples, and is often barely visible unless you hold the barrels at the right angle to a light source. There are several theories as to what causes it, from shot bridging, to gas hammer, to a partial blockage of the bore caused by a shot-filled wad trying to displace excessive oil as it moves down the bore. I personally think the excessive oil in the bore theory is the most plausible considering the hydraulic forces that might be generated in that scenario. There is a pretty good discussion about rivelling in "Shotgun Technicana". I have never heard of any problems that arose strictly from firing a gun that has rivelling, and wouldn't hesitate myself unless barrel wall thickness in that area was marginal.

Ring bulges in the choke area, some of which were reported with steel loads (especially early ones with less protective wads) being shot through tight chokes, are pretty much a cosmetic issue. Pressure is so low out there that nothing is likely to happen. They're unsightly, but not very likely that they're dangerous. After all, we shoot guns with holes at the muzzle (porting) without any concerns.

Someone earlier suggested that a bulge within the first 18" or so is a definite cause for concern. I'd agree. I'd also agree with Miller that fixing dents is often fairly easy. I used a hydraulic dent lifter on quite a few, always being careful not to bulge the barrel.

I made a set of expanding dent plugs for 12, 16 & 20 gauges on my lathe. They have worked extremely well for me.

I have told this numerous times before but once more. I bought an H grade Lefever parts gun which had a crack in the left barrel 14" from the breech. This gun had barrels of what Lefever described as "Best London Twist". The crack followed a weld line but did not appear to be an actual separation of a weld, just followed beside it. The appearance was that it had been struck on a hard object with a sharp corner which caused the crack & turned a section inward, inside the bore. Appears it was likely then fired with this inward obstruction which raised a flap on the opposite side of the crack to the inward flap. Probably enough pressure escaped to prevent it bursting.

Using my home made dent plugs I raised the inward flap & hammered down the outward one. The two sides fit back so perfectly I doubt any one would even notice the crack unless told specifically where to look & then it is very hard to see. Did "Not" appear to be any stretching of the metal at all.

After this I proceeded to fire (Remotely) several factory loads of 3�DE-1 1/8 oz loads & then several 3 3/4DE-1� oz factory loads. I then fired several 1 3/8 oz reloads. None of the above opened the crack at all nor did any sooty smudge appear on the outside of the barrel. That was a number of years ago & even knowing exactly where this crack is iit is hard for me to find it even all these years later. The entire bores of this gun were extremely pitted.

As I said earlier these old "Welded" barrels are simply not the "Death Traps" many have been led to believe

+1 for 2-p. Good discussion.

When steel is stressed beyond its elastic limit (the point of permanent deformation), it will suddenly yield slightly and then require an increased stress for further yield. This is called work hardening and is easily demonstrated by "bending" a coat hanger wire repeatedly. The wire will not continue to bend at the original location unless forced to do so. That is, the metal at the original bend has become harder/stronger and causes the bend point to move up/down the wire length.

If the bulge/dent is of modest size and has not exceeded the local metal's ultimate stress (the point where the metal suffers a fracture), it is usually possible to work the metal more or less back into place. Anyone undertaking b ulge/dent work should have a good knowledge practical metalurgy.

I would expect that only a severe dent could act as a bulge causing obstruction. The obstruction must be of a size and/or mass to create a gas hammer which then creates a bulge.

There are a lot of factors involved in a barrel burst. All steel is not created equal, barrels are not made equal, and barrels do not have a single common stress history. Thus said, it is not really practical to write a simple set of instructions for do/don't work on bulges/dents.

DDA

I have read all of the replies to my questions and appreciate them. The information sounds logical to me and is what I want to hear. Logic, of course, is not science so I reply this way. It seems there is a common thought that dents and repaired dents are less of an issue than bulges and repaired bulges? My thinking is, a dent is bulged in not out? A "bulge" is most often cause by an obstruction and pressure a dent by an impact. The "work hardening" would apply (positively) in either deformation? Leaving then; a dent is not an issue unless it obstructs the bore and a bulge is not an issue -unless it allows the wad to become an obstruction?

I am going on with this because of opinions I have read that basically say fix a dent, scrap a bulge.

The fellow that fixed my two dents charged me for five dents. Three, I didn't see obviously? Neither of us saw the bulge.

An obstruction is certainly a problem. Not long ago, I believe Toby B. commented on these forums about the various proof failures he had experienced over the years. Bulged barrels were mentioned specifically. Of any incident that created a bulge in a shotgun barrel, it's probably safe to conclude that an obstruction would be documented to be not presents, and the specification accuracy of the ammo should be beyond question.

If it can happen under the controlled conditions of proof testing, maybe over pressure alone can cause a shotgun barrel bulge out in the general shooting community.

Don, is it true that, given equal obstructions, one nearer the muzzle is more likely to cause a burst barrel, than one nearer the breech? My reason for asking is that it would seem that the more air that is trapped in the barrel, the more severe the air hammer will be.

A barrel that has been jabbed into the mud, then fired, will likely burst or at least have a severe split and/or bulge. However, years ago on here we had a poster who taught kids to shoot in some type of structured setting. He said he wanted to show what occurs when you drop a 20 ga. round down bore in a 12, then chamber and fire a 12 in it. He did so from a remote location, several times, with no bulges or burst barrel, and was incredulous. Most of us who read it were, too.

I realize all that is only anecdotal, but does it support my question in any way?

SRH

Barlow's bursting formula P=2 S 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.

Burrard used the Alger Burst Formula
Burst pressure = Ultimate tensile strength x 3(OD � ID) / OD + 2xID

All the burst formulae refer to a pipe capped at both ends with a static pressure (a pressure cylinder). Shotgun barrels are not designed to be pressure vessels as one end is open and the pressure rises and falls quickly.

The Hoop Stress Formula doesn't reliably predict shotgun barrel failure either
https://www.engineersedge.com/material_science/hoop-stress.htm
Shotgun barrels are �thin wall cylinders�
stress = pr/t
p= pressure; r is the inside radius; t is the wall thickness

Barlow's (and the other formulae) DO work with a totally obstructed barrel. When the "critical confluence" of variables meet, the barrel bulges or bursts.

At least by the images I've accumulated, the point of the obstructional burst (not counting mud/snow in the muzzle) seems to be 6-12" from the breech





jOe's indestructible 4140



Thin barrel splits seem to be mostly 14-18"





And over-pressure loads blow out the breech

Obviously those barrels which Bulged in proof were not likely to have been obstructed. I "Believe" that normally proofing is none with a powder designed to stress the forward portion of the barrel to a greater extent than would be done with normal shotgun powders. My take would be the proof load exceeded the elastic limit of the steel at the point it bulged.

I would also expect that fully 98+ % of barrels bulged in use, either hunting or clays were caused by an obstruction. Also keep in mind that when an obstruction is hit the pressure in entire bore area behind the obstruction is not raised to the same level as At the Obstruction. You get a localized pressure spike near the obstruction, depending upon the severity of the obstruction. In some cases the bulge will actually occur a bit forward of the actual obstruction, showing the obstruction was moving before the pressure spike occurred, the gases simply caught up with it.

In the case of the Lefever I mentioned I feel the "Dent" was severe enough to cause an obstruction. I cannot think of any other reason the side opposite the crack would have been raised. Personally "IF" a barrel of mine gets a dent, I want it raised. I'd rather be safe than sorry.

At a local gunshop that I frequent, a very nice Browning o/u came (can't remember the ga.) in with both barrels bulged just in front of the hand guard. We all speculated about the cause and it eventually came out.
The fellow had been using sub guage chamber inserts that left a powder fouling build up/ridge at the point of the bulges. This fellow didn't clean the bore before he went back to shooting regular ga. shells and the barrels bulged. The general consensus was that he scrap the gun.

The posts and pics raise the issue of repairability. It is hard not to think of the ease of barrel replacement in the Baby Bretton (hand screwable ribless barrels). Especially when seeing how damage to one part can write off the whole barrel assembly in conventionally built guns. The design challenge would be to incorporate that kind of repairablity in something prettier cause the BB is undeniably ugly.

What Miller said

A study by the Royal Military College of Science, sponsored by the Birmingham Proof House and the British Association for Shooting and Conservation, showed that an obstruction by 2 fibre wads (total weight of 4 grams) was sufficient to bulge or burst a 12 gauge barrel shooting a 28 gram (slightly less than 1 ounce) load. Peak pressure occurred 22mm (.866�) past the leading edge of the obstruction.

And more from Burrard
If the burst was not caused by an obstruction it must have been the result of some excessive pressure or of some abnormal weakness in the barrel. A (excessive load) pressure burst can only occur in the immediate neighbourhood of the chamber; and so if the burst occurred ahead of the chamber cone an excessive pressure can be ruled out.

Another chamber burst



BUT an asymmetric ring bulge related to the addition thickness of the brazed barrel flats and support of the right barrel. The burst was likely a wad in the forcing cone



Federal 10g with 2 piece fiber base wad

While we're at it, properly designed and fabricated shotgun barrels, manufactured with the appropriate steel do NOT undergo low cycle fatigue; elastic deformation when the yield strength is exceeded.

This obviously is not a shotgun barrel but demonstrates the "waves in the sand" fatigue striations



150X SEM with fatigue striations transitioning to "fisheye" elastic deformation (stretching) then to cleavage



As said, I only play a metallurgist on DoubleGun and for additional light reading:
http://www.martin-moeser.de/Images/Fractography.html
https://www.efatigue.com/training/Chapter_3.pdf

Mr. Hause. As I read your posting I wanted to ask; all shotguns that fail proof in British proof houses would then fail at or very near the chamber, correct? Is there a way to know this for sure? Can it be safely said that any barrel burst further down the barrels must be due to an obstruction or structural defect ie the metal is defective in a significant way? I am really trying to get a handle on this idea that dents are minor bulges are major. Thank you.

In 2006 the British Rules of Proof were modified to apply increased pressure further down the tube
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).
The target pressure at 6" and powder used is a Proof House secret

1929 Hunter Arms Proof Load Pressure Curve Chart
http://library.centerofthewest.org/cdm/singleitem/collection/WRAC/id/8149/rec/107
12g 2 3/4� was proved with 6.5 Drams FFFg with 1.687 oz. shot = 14,200 psi at 1�; pressure at 6� was about 9,500 psi.
Pressures were measured by crushers (LUP - Lead Units Pressure) and modern piezoelectric transducer measurements would by 10 � 14% higher

A barrel that is dented 6" from the breech received significantly more force than one dented 6" from the muzzle; likewise a bulge 6" from the breech would be a major concern, 6" from the muzzle a minor concern. Make sense?
What the metal deformity looks like microscopically with either a dent or bulge requires a photomicrograph, with destruction of the barrel.

I would suggest "minor" or "major" is primarily a function of the location of the defect, and the wall thickness of the tube at the defect. And that can be measured without sacrificing the barrels.

Might as well mention "Zircon's" metallurgical failure analysis on the Sherman Bell Parker VH fluid steel and GH damascus barrels. His full report and the images are copyrighted, but this is his post from 2007

http://www.familyfriendsfirearms.com/forum/archive/index.php/t-55364.html

The extractor screw hole acted as an initiator and low cycle fatigue did occur with increasing load pressures until cleavage

Thanks, Don.

SRH

Burrard reported on obstruction tests which were done with a hollow obstruction which resulted in as severe a bulge as an equal weight solid one. This definitely showed that it was not the trapped air ahead of the charge that caused the bulge, but the Gas Hammer behind it as Don said.

He also reported on some cases where the bulge was closer to the breech but not severe enough to cause a burst. In some of these tests two or even three ring bulges were produced. Each moved further down the barrel & were less severe than the first one. This was explained as the result of those Shock Waves Don mentioned as they bounced back to the breech, then forward again to catch up with the still moving charge & produce another bulge. These tests were performed in a barrel tapped for a crusher pressure gauge. In no case was the initial max chamber pressure increased from that of the normal shell being fired. Firing a 12 gauge shell with a 20 gauge one lodged in the forcing cone would raise the chamber, but an obstruction further down the barrel does not, just creates that localized pressure hammer.

What Miller said

TWO left barrel bulges. The proximal bulge is at 4 1/2� with a bore enlarged to .758� from .735� at 3 1/2". The wall thickness at the bulge of .077� compared to .090� on the right.



Major Sir Gerald Burrard in the second edition of The Modern Shotgun (1948), Volume 3, The Gun and The Cartridge, �The Diagnosis of a Burst� discussed �Wave� Pressures and the etiology of multiple bulges pp. 364-375.
p. 365
When the explosive charge was placed entirely at one end of the closed vessel (discussing experiments by Paul Marie Eug�ne Vieille and published in Etude des Pressions Ondulatoires in 1890) the gases given off naturally rushed forwards along the length of the vessel until the forward layer of gases was suddenly checked by the closed end. When this occurred the gases which were behind the extreme forward layer over-took this layer and began to pile up against it, with the result that the extreme forward layer was compressed with great violence. It was this compression of the extreme forward layer of gases which caused the high pressure�
p. 368
Since this wave pressure acts radially outwards the wall of the barrel is submitted to a very severe pressure all round its circumference, and if the pressure is sufficient to stress the barrel beyond the elastic limit of the steel a permanent bulge all round the bore is the result. Such a bulge is knows as a �Ring Bulge� �
p. 374
If the wave pressure was not sufficient to burst the barrel...the shot charge and obstruction will continue to travel along the bore under the influence of the expanding powder gases, but the wave pressure will be reflected backwards and will occur again at the extreme end of the cartridge-case. It will then rush forward once more (third wave) and may overtake the shot charge�in which case it will act again immediately behind the wads.
It is possible for the third wave pressure to be sufficiently violent to bulge the barrel some way ahead of the site of the first wave pressure, in which case one obstruction would be responsible for two ring bulges.

New fangled steel barrel with 3 bulges

Has there been any conclusive work done with cartridge detonation, the phenomenon of the propellent fracturing, or turning to dust, and becoming an explosive in the chamber?
This one scares hell out of me, I can measure chambers and barrels, but, I have no idea where some of the ammunition around the place has been or what it has been exposed to.

Best,
Ted

I think there're a few interesting points, but overall, it's another example of documented bulges without an obstruction, at least as described. Maybe, because of the gas hammer theory, all bulges and bursts are 'ring' bulges to different degrees, and only appear asymmetrical to the degree that the hoop in the area was asymmetrical.

I think there're indications here and there that point to non obstruction bulges. I still know obstructions are a problem, but they may be attributed to more incidences than they might be responsible for. We tend to see examples in larger bore guns. Maybe, a relatively long duration in a relatively large cylinder allow occasional unlucky coincidences of the wave, gas hammer theories and relative localized weak points?

edit to add, I see now that Doc Drew likely added the actual reference pages and references to obstructions.

Here you go Ted.
DDT HAS been demonstrated to occur with Smokeless Powder in an experimental setting.
To my knowledge (and I suspect the powder makers ain't sayin') it has NOT been demonstrated to occur in a shotshell
http://www.trapshooters.com/threads/smokeless-powder-ddt.245629/

Some humble opinions and SA sniping by the usual suspects here
http://www.trapshooters.com/threads/there-is-another-possibility-with-a-gun-blowup.50956/

http://www.trapshooters.com/threads/shotgun-blowups.244114/

I can't help noticing that the photos of ring bulge damage attributed to gas hammer doesn't even remotely resemble rivelling.

I'd also think that the risks associated with propellant fracturing wouldn't be as likely to occur in a shotgun shell because the powder charge is held firmly in place by the wads, shot, and crimp. The cases I've read bout with rifle ammunition have resulted when cartridges rolled around and were subjected to prolonged vibration as when laying on the dashboard of a pick-up truck for many miles on rough roads. This probably wouldn't be much of a problem in rifle or handgun ammunition that had compressed powder charges.

Friction has two differing values; static and sliding. Typically, static friction is higher than sliding. If an increasing force is applied to an object sitting statically on a surface, the object will not move until the force rises to above the force of the peak static coefficient of friction. The object will usually experience an acceleration due to force above the sliding coefficient of friction. If the force then drops back below the peak force of static coefficient of friction (the object outruns the force source), the object will decelerate. This is called stick-slip friction and is a common event. Stick-slip is the cause of tire squeal.

The wad and shot travel down the bore may not be quite as orderly as we usually envision. In the case of a bore and shot size prone to shot bridging, it may be that shot bridges form and collapse a number of times. The bridge causes a stick and the collapse leads to a slip. If the stick phase is severe enough, it may cause a mild gas hammer. The hammer may well collapse the bridge leading to a slip phase. If a second bridge forms, the foregoing cycle may be repeated. Rivelling? Maybe.

DDA

If a pressure wave theory is valid, Doc Drew cited above that it can be reflected. Maybe, rivelling and other bulges can occur by random additive wave interference, and not necessarily an obstruction. Classic game guns may be intentionally struck or may acquire unintentional hoop strength reductions that just aren't seen as commonly in thicker and tougher modern barrels. Could that make them a bit more susceptible to a random wave amplitude that might approach double of what was intended?

This discussion reminds me of the sonic shockwave effects on 2 cycle tuned expansion chamber type exhaust pipes. The sonic shockwave has enough energy to actually reverse the exhaust flow of an over scavenged cylinder, and push the mixture back thru the exhaust port, into the cylinder, effectively supercharging it. There are some common gas dynamics effects. The elevated temperature raises the local speed of sound significantly in both cases.

At least you know what you're talking about...

Wow, did that ever bring back motocross memories from 40 years ago!

Mike

Yeh, having the motor/engine running as they say "on the pipe".
Karl

Reminded me of the smell of Klotz, hadn't thought of that for quite a bit.