So... barrel steel discussion here?

[Eric Kettenburg]

How much does the processing (drawing to new shape vs stock removal) and stress relieving of 12L14 affect the properties important for integrity in use as a ML gun barrel?  Are we tending to lump all 12L14 barrels together here?

That's a very important question, especially considering that there have been (historically, i.e. over the past 50 years) multiple ways the manufacture has been accomplished:  the drawing to octagonal shape, the screw-press method (was that Paris?) and the most common method [for tapered/flared barrels) which seems to be turning down to progressive diameters on a lathe, then milling flats.  There might be others of which I'm not aware.

Rich I'm only serious some of the time.  The other half, probably not...  I do get kicks out of a good brouhaha.  Sorry!

[rich pierce]

Eric

I'd think that this could be done safely, but I would take it seriously.  Number of threads per inch matter, finish on the threads matter, and the torque spec matters.  Otherwise, there should be enough steel there to do this in a reasonable manner.  Talk this over with an engineer.  The calculations are straightforward, and whatever the engineer charges you is money well spent.

Rich - Sorry for the digression but I'm all done with this now.  This is a straightforward mechanical engineering problem, and doesn't need a whole thread of its own.

Jose, no problem. Perhaps some engineer could comment on whether on those long barrels with a threaded joint in the middle, the pressure has reduced by the time the ball gets to the joint?  Say 30" from the breech. My limited understanding is that pressures are highest at the breech at the time of ignition, and as the ball and charge gain velocity the pressure diminishes.

[galudwig]

Perhaps, someone could find an engineering student who's also interested in muzzleloading to take on such a project as a masters or doctorate subject.

In terms of a study along the lines of what Eric is asking for, it would seem most relevant to seek out shooters that can document claims of having shot 10-20,000 rounds from a 12L14 barrel and offer to buy them back so that an engineering student can look at them. I'm sure that if a mounting a new barrel (of their choice) to their rifle was also offered in addition to buying back the "used" one, there would be takers interested in furthering the cause. Heck, I bet the Marsh Family from KY could even supply sample barrels. For as much shooting as they do and after years of dominating offhand matches at Friendship, I'm sure they have gone through plenty of 12L14 barrels.

Someone else here mentioned they didn't know how to simulate that many rounds fired through a new barrel. Using "real" barrels that have been heavily used for years would seem to give the most accurate representation of the affects of pressure over time.

So, after 4 pages of discussion, the two take-home points for me are:

A) No one has done a study of 12L14 muzzleloader barrels to determine the effects of repeated firing on the steel over time, and..
B) The vast majority modern-day muzzleloader shooters are cheap SOB's unwilling to pay for barrels made from steels deemed to be suitable for gun barrels.

There is a lot of quoting of metallurgical properties of different steels going on here and these are things that I have neither the knowledge nor the desire to comprehend or refute.  There are also lots of facts being woven into passionate arguments aimed to convince me that I shouldn't be shooting barrels made of 12L14 steel.  However, no one has definitive proof (backed by studies such as Eric originally asked about) that I shouldn't be either.  The bottom line for me is that if 12L14 steel is such a bad choice (safety-wise) for a muzzle loading rifle barrel, why does it continuously defy the laws of physics and logic? Physics and logic suggest that barrels made of 12L14 steel should be failing at a high rate, but they are not. 

A researcher may examine a used 12L14 barrel and find that the steel has become brittle and unsafe after 10-15,000 cycles.  Then again, that researcher might examine a used 12L14 barrel and find that there is no change at all in barrel steel integrity after 10-15,000 cycles.  We just don't know and all the speculation in the world doesn't make it so. My only point is that until you explore Take-Home Point A, there is no definitive proof that makes Take-Home Point B necessary. To me, definitive proof can come only after examining barrels that have been in constant use over time.  If someone shows me definitive proof that I'm at (increasingly) serious risk every time I fire one of my 12L14 barrels, I'll retire them. Until then, I guess I'll have to stand among the ranks of the cheap SOB's willing to take unnecessary risks. 

[JCKelly]

Tensile strength of anything is not a major issue with contemporary muzzle loader barrels.

The effect of repeated firing would not, I believe be important unless the barrel had a crack, seam, or other notch to begin with. The crack, or crack started at a notch, may grow each time the metal is stressed.

That is what happened to the gentleman who lost all but little finger & pinky on his right hand. Barrel had been proofed, shot an estimated 200 some times with black powder. A piece recovered later showed the thing had a rather long, deep crack in it.

It is not tensile strength.

It is toughness, the ability NOT to crack at a notch. A notch may be a long seam in the metal, not uncommon in your favorite barrel steel, or poorly designed breech, or too very deep a dovetail. In Remington shotguns I believe it was some stamping near the breech, at least for the earlier failures.

Tensile strength is not the issue.

Barrel steels in use have sufficient tensile strength.

[boman]

Just to add to the discussion: Dan mentioned Remington and trap shooters. I personally know of a Remington 1100 that cracked after 250,000 plus rds. personal friend named Dave Chapman bought the gun new early 1970s--cracked late 90's. Remington sent him a new gun Sometime last year a Krieghof failed at the breech(top barrel If i recall) at a registered shoot in Kokomo Indiana. A friend of mine was there and showed me the pictures(he didn't know the round count and no there was no obstruction in the barrel). Dan also mentioned machineguns and VietNam.  Army recommends depot check for lug crack on M-16 bolt after 5000rds. (Carpenter 158 Steel).
Point---All steels can fail and that steel work hardens just like non-ferrous metals.

As far as Eric's question concerning pressure 10-12 inches from breech(threaded portion from what I understand on long barrels).  FWIW I shoot a smokeless muzzle loader---custom rifle on a Remington 700 receiver(4140 barrel) and the strain gauge testing that has been done with these guns shows that the pressure drop that far from the breech is a lot---something like dropping from a peak of around 45000-49000psi,depending on the load and powder, to well under 30000psi maybe more if i recall) with a single powder(some guys are using booster charges of a faster powder and getting a double peak but the second pressure peak is very much lower. This information is posted on Doug's message boards if you want to check my numbers---I'm too lazy at the moment.

Carry on---Steve

Steve

[Mad Monk]

Back to barrel steels:  it seems to me much of the data and most or perhaps the critical incident(s) with 12L14 were with Douglas barrels which it seems may have accumulated additional stress from being drawn to octagonal shape. Perhaps most agree at least this was an additional variable.

I am thinking of barrel makers contemporary with Douglas barrels; GRRW, Sharon, and Paris come to mind. I seem to recall Sharon button rifled their smaller calibers then stress relieved the barrels.

How much does the processing (drawing to new shape vs stock removal) and stress relieving of 12L14 affect the properties important for integrity in use as a ML gun barrel?  Are we tending to lump all 12L14 barrels together here?

The early debate on this subject of barrel steel goes back to the days of the Buckskin Report and Black Powder Report.  At that time the one manufacturer who had most of the problems was T/C.
By 1984 T/C had contracted with a university to look into the failures of their barrels.  They claimed that only the use of smokeless powder or smokeless admixed with black could burst their barrels.  The university lab then proved this.  Or thought they did.  When I read their report I went to work in my lab.  They claimed they had irrefutable laboratory proof that only smokeless powder could blow up one of their barrels.  They would wash the broken barrel parts with acetone to dissolve any traces of smokeless powder or to pick up lower oxides of nitrogen from the pores in the metal.  The claim was that black powder is not soluble in acetone while smokeless powder is.  The barrel washings were then dried, acidified and checked with diphenylamine.  The same test method police used to look at a person's hand to see if they had fired a gun.
But when I looked at the university lab's work I knew right away it was questionable.  In some tests they would use du Pont black powder and GOEX in other tests.  Now in 1984 the chances of some guy being handed a can of du Pont black powder with a new T/C Hawken rifle were nil.  So why the switching back and forth.  The end result was that they simply proved that GOEX black powder, and NOT smokeless, had been used in the guns where the barrels blew up.  I then confronted the two from the university that played this slight of hand.  Was treated to some fancy footwork back pedaling.  According to their test method.  Every time I shot my GPR at the range I Had burned smokeless in it.  The "proof" of smokeless test gave a higher positive in my bp rifle than in my Mini-14 after a 30 round mag firing.  When GOEX bp out of Mossic is run through that test it gave a very strong positive in the test.  The chemical decomposition in the powder gave lower oxides of nitrogen from the potassium nitrate and that is what their so-called proof test looked for.  But they used the du Pont in any work that would be followed by the acetone wash.

[davec2]

As reluctant as I am to jump in here again, I have two comments and a couple of general questions.

Comment #1:  To JCKelly about rocket failures in the 1960s......you don't know the half of it.   I have worked building engines for the Space Shuttle, Atlas, Delta, Peacekeeper and a host of other spacecraft and weapon missile systems since 1981.  We have exhaustively tested a myriad of metallic and non metallic materials to their absolute limits tens of thousands of times during development programs, often times with almost unlimited budgets.  However, added to the design complexity for us, our hardware has to FLY, so it cannot be built to ASME boiler code with safety factors of 4 or greater.  And, many of the systems are man rated....someone's life depends on the hardware working without failure.  While rare, we still have had failures anyway.  I understand what you are saying about tensile strength, toughness, etc., but I have used the very best material that any amount of money can buy and designs that unbelievably concentrated brain power can devise.....and still had the @!*% thing fail.  Material flaws will always occur.  Some number of gun barrels will always fail for various reasons no matter what material they are made out of.  If the object of the game here is to select a useable material that will not fail as a gun barrel under ANY circumstances, I respectfully submit that there is no such material.

Comment #2:  To Galudwig....I love your two take home points ! (Especially B)  But with regard to point A, Dan noted in a previous post that even a thorough test program would not tell you much because it might be the very next untested barrel that would fail or the one you tested to 15,000 rounds would fail on round number 15,001....so...probably not worth doing the testing.

Question #1.  How many people on this very board have had a barrel (made out of any material) fail ?  (Not heard about a failure....actually had one and under normal circumstances....i.e. not triple loaded, bore full of mud, "I only used 330 grains of BullsEye....I don't understand what happened !....  etc.)  I think that this very group of builders, shooters, barrel makers, barrel users....many of whom have years and years of experience and who have fired thousands and thousands of rounds through all types of barrels...we are the best data base available....and, most importantly, we all get one another's opinions for free ! 

Question #2.  I can understand why they might not want to participate here, but of all the current manufactures and / or sellers of ML barrels (Chambers, Getz, Rice, TOW, Colerain, etc.) how many have had legal issues resulting from a failed barrel ? (As far as I am aware, none of them has been sued out of business in many years....am I wrong?)

Question #3.  For Dan....for the guns you build, what kind of steel are your barrels made from and where do you get them?  If I don't want to use a 12L14 barrel, what are my options?

Thanks

[galudwig]

Tensile strength of anything is not a major issue with contemporary muzzle loader barrels.

The effect of repeated firing would not, I believe be important unless the barrel had a crack, seam, or other notch to begin with. The crack, or crack started at a notch, may grow each time the metal is stressed.

It is toughness, the ability NOT to crack at a notch. A notch may be a long seam in the metal, not uncommon in your favorite barrel steel, or poorly designed breech, or too very deep a dovetail.

So, is it safe to say that:

A) Any barrel (regardless of the type of steel used in it's construction) can fail if it has a crack, seam or notch in it,

B) Some barrel steels (by their nature, make-up, and/or manufacture) are more likely to start out with a crack, seam or notch in it, and...

C) Some barrel steels (by their nature, make-up, and/or manufacture) resist cracking at the flaws better than others.

If this were true, then it seems plausible that you could stuff all those metallurgical factoids into some sort of equation that would tell you how many times more likely a 12L14 barrel would fail compared to one made out of something like 4140. While that would be useful information for those concerned with barrel safety, it still doesn't explain why 12L14 barrels aren't failing as often as the numbers say they should. I'm beginning to wonder if there is really any practical way to determine that.

As for proofing, I always wondered why you would call it "good to go" if a double charge didn't blow the barrel?  Yeah, it might have held for the proof load, but was it the proof load that started the crack in the barrel that eventually led to the guy losing his pinky or was that crack there to begin with?  Who can say definitively?

After reading davec2's last post, all I can say is "Amen!" Don't think I can add much after that, so I think I'll crack a cold one, sit back and enjoy the rest of the show! 

[Joe S]

Rich and Eric

Here's an estimate for barrel pressure at different distances from the breech for a 12 bore.  The assumptions in the calculation are 1) peak pressure is 15,000 psi 1" from the breech face 2) no pressure is lost out of the vent, and 3) pressure is directly proportional to volume (Boyle's Law).  Units are inches from the breech and PSI. 

1"   15,000
2"   7,500
6"   2,498
12"   1,249
15"   999
24"   624
30"   500

A note on proof testing – If the proof test is correctly designed, it can predict barrel life, but only if the barrel diameter is measured very accurately before and after the test.  Without the measurement, all you have learned is that the barrel did not fail that time.  The test cannot take into account changes in the steel properties, such was work hardening, or the future behavior of a hidden flaw.

If you’re interested, look up fatigue limit and yield point.  This is a complex topic, but these are the basic principals involved.  As JCKelly pointed out "The information is out there. All you have to do is let it in".

[FlintFan]

If I don't want to use a 12L14 barrel, what are my options?

That is really at the heart of this debate.  Unless Green Mountain resumes production of swamped barrels, there are no other options for them other than ones made from 12L14.  If you are looking to use straight barrels, you have a couple choices, but not for swamped. 

If there was a barrel maker who switched to a true gun barrel steel for swamped barrels and everyone flocked to him for their barrels, other makers would follow suit.  Green Mountain tried it, and apparently discontinued production.  If it was profitable it would be assumed they would still be in production. Maybe if there is enough demand they would re-introduce them...

[JCKelly]

Couple of things.

If you really want to know why I say "tensile strength is not the issue here" look over

https://www.linkedin.com/pulse/historical-failures-evolution-fracture-mechanics-ajay-taneja

Designing on tensile strength got a lot of people dead in Boston, and a couple hundred Liberty Ships sunk in WWII - at least one just broke in half while resting in harbor. Argue all you want about it. This is life where steel is concerned. Steel is not brass, it is not even wrought iron. Steel is steel and it behaves in its own way

Much of this is beyond me technically. The part that might be clear is -

LIBERTY SHIP FAILURE: BRITTLE FRACTURES AND THE BIRTH OF FRACTURE MECHANICS

Some kinds of steel can withstand a notch or crack better than others. To my recollection, I saw only one "fracture mechanics" test result on 12L14, and it was about the same number as a real good ceramic. Good ceramic, bad ceramic, who cares.

It is hard to get any steel mill to clearly define what they mean by "Gun Barrel Quality" and "Rifle Barrel Quality" steel. Lawyers/litigation/lawyers/lawyers/lawyers
make them leery. They tend to wave their hands a lot when asked. My one experience with this was when my employer had an order for 416 stainless (free-machining, magnetic stainless used in firearms). The US producers barely waved their hands. The Swedes, who are handicapped by having native honesty, at least gave a verbal description. Without being too cynical, GBQ or RBQ steel is some grade to which sulfur has been added so the barrel maker can machine it faster, yet has been carefully produced and tested so that all that sulfur doesn't (isn't supposed to) glom all together in one place, and the bar hopefully has no seams in it. Responsible MODERN riflemakers magnetic particle inspect each barrel for seams, even those below the surface.
As others have said, a small barrel maker just can't get a hold of this product in lots of under one zillion pounds.
Well, the next step . . . since I don't want to get sued, either, hmm. Why doncha
start out looking under, say www.aerospacemetals.com/
One example of what they carry is E4130 Aircraft Quality bar.This is approximately the steel used in good shotgun barrels, such as Rugerwhentheymadethem, Browning, definitely not unmentionabletoavoidlawsuit.
This is just an example for your perusal.

" E4130 Aircraft Quality Bars

4130 is an electric-furnace, through-hardening, chromium-molybdenum alloy processed to meet the rigid standards of the aircraft industry and vacuum degassed to conform to the magnetic particle inspection standards of AMS-2301. Its excellent weldability, formability and temperate hardenability predispose this alloy to a wide range of applications. Normalizing without liquid quenching increases its strength sufficiently for most uses; however, it may be heat treated for greater strength. It may be nitrited for maximum wear and abrasion resistance.

 Applications

Type 4130 finds exceptional use where extremely high strength and hardness are required from relatively thin sections. It finds major use in applications requiring welding. It is extensively used in the aircraft industry for parts and components. "

A number of warehouses carry this stuff. Don't know what their minimum order is but it sure is not a mill heat.

That is it. Time for dinner

 


 

[stuart cee dub]

Much of this discussion is several levels above my pay grade so this may be a simplistic question.
 If one were using barrels made out of 12L14 would going to a thicker barrel wall or just a heavier barrel period be any safer?

Remington back in the 19th century made barrels of cast steel which were quite heavy for caliber and sold widely.
Maybe they were compensating for imperfect or brittle steel through sheer mass?
 

[Bob Roller]

Much of this discussion is several levels above my pay grade so this may be a simplistic question.
 If one were using barrels made out of 12L14 would going to a thicker barrel wall or just a heavier barrel period be any safer?

Remington back in the 19th century made barrels of cast steel which were quite heavy for caliber and sold widely.
Maybe they were compensating for imperfect or brittle steel through sheer mass?

I had a fine heavy 40 caliber with a 1 and 1/8 octagon marked on the bottom flat "Remington Cast Steel"
and on the top,N.G. Whitmore, The rifle was a butt stock style,no fore arm,fine wood and silver trim.
Butt stock configured exactly like the Whitmore made for General Grant in 1866. Sight was a telescope
full length of the barrel.I don't think any normal load would be a threat in a 12L14 barrel of this caliber.
A 13/16 in 45 caliber is another proposition.

Bob Roller

[JCKelly]

Unfortunately where toughness is concerned, thicker is, if anything, worse. Not sure why, smart metallurgists could tell you. But thin things are tougher than thick things, with the same chemistry and strength.

Here is a paragraph I forgot to include in my last post, mostly fyi:

E4130 Aircraft Quality Sheet and Plate
Type 4130 is an electric-furnace processed, chromium-molybdenum aircraft quality alloy used primarily for welding or where moderate tensile strength is a requirement. The careful processing it undergoes completely eliminates the possibility of seams, grooves, pitting or blistering. It also undergoes diligent inspection and rolling to insure its freedom from lamination and tears. It is available in the normalized or annealed condition, and maybe pickled and oiled.

Emphasis mine.

Someone asked how about plain old 1018? Well, it is good stuff, better than was used back in the day. Two problems. No one, so far as I know, makes this stuff processed to avoid all cracks or seams. Steel bars don't have seams very often but they in deed do have them on occasion. That is OK, so long as you have your own magnetic particle inspecting machine. Second, 1018 is always cold drawn to give better strength and machinability. This, too is OK except the stuff is full of residual stresses. To make any sort of barrel out of it one must first anneal it about 1100-1200F to get rid of those stresses.   

[davec2]

Hey.....at the risk of throwing a hand grenade into a powder magazine here....has anyone here asked Steve Bookout about how his 100 + hand forge welded barrels have panned out for reliability ?   

 

[Joe S]

It seems to me that most of the barrel failures people cite were in the 60’s and 70’s.  Is that true?

Are there recent (last 20 years) examples of barrel failures that are definitely not due to smokeless powder, short started balls or other misuse?

Given the litigious nature of our society, I think normal use barrel failures must be exceedingly rare, simply because a small manufacturer could not afford very much litigation.  One good lawsuit would likely put them out of business.

Are there any manufacturers out there who are willing to comment on this subject?

[Eric Kettenburg]

I think you would be very hard-pressed to get any type of information like that out of a barrel maker.  This being said, I also suspect that you are correct in that I don't think in more recent years (I'll arbitrarily say 1990s onward) there have been any that I recall hearing about, *save* a couple of verified incidents with the barrels made from hydraulic tubing and one incident of which I'm aware involving a pistol barrel turned down from bronze bearing stock.

[conquerordie]

Where these the muskets from India? I don't know all the stories with them, something about fouling and bad breechplug an such. As with 12l14 barrels, there are a lot of those muskets, and other manufacturers that used DOM and some shoot them all the time with no problem.
So from this discussion I've read that just about all materials modern day barrel makers and gunsmiths use in the muzzleloading field are incorrect on paper, but seems to work on the field under responsible shooters. I'm still waiting on the opinions about the two piece barrels. I've met a couple of reenactors with them in a HVF and a French Buccaneer. Both shot them without any fear.
I have used Getz, Rice, Colerain, Rayl, and shot DOM from a friend's gun. I didn't fear any of them. Even the most questionable, DOM Indian guns, don't fail at alarming rates, or theyd  be out of business by now. On paper we should fear all these barrels, and yet we are all still here. I've learned many things about barrels in this conversation, but after five pages, nothing has changed.
Greg
PS I'd shoot a hand forged barrel from a modern day builder like Colonial Williamsburg without hesitation as well.

[Eric Kettenburg]

I'd like to clarify, also after 5 pages of GOOD and polite discussion.  I did not want this thread to turn into some kind of public bashing of any/all modern barrel makers.  Nor did I necessarily think it would turn into an all-out war over 12L, and I think I mentioned that pretty clearly at the beginning (it is, and remains, controversial).  I was hoping to get some metallurgical information, simply to see what might be 'out there,' and also was hoping for some type of long term or repetitive use study that apparently does not exist.  Thanks very much to all who posted for a really detailed, good discussion.

[Joe S]

conquerordie - There is sufficient steel at the octagon to round transition to make a safe screw joint.  Important considerations are threads per inch, torque specification and thread finish.  These calculations are straightforward and you can find the equations on the net.  Better yet, consult your friendly local professional engineer.  My main concern would be long term corrosion.

Eric - Agreed.  This conversation has been both polite and useful.  Thanks for starting it.

Barrel Makers - Are you paying attention?  There is a market for gun barrels made from more appropriate steels that have been properly heat treated.  Green Mountain can produce them at the same price point as 12L14, but that's Green Mountain.  Since GM swamped barrels are no longer available, and they never made fowler barrels as far as I know, I think you could certainly get a premium for these barrels.

[T*O*F]

Barrel Makers - Are you paying attention?  There is a market for gun barrels made from more appropriate steels that have been properly heat treated.  Green Mountain can produce them at the same price point as 12L14, but that's Green Mountain.  Since GM swamped barrels are no longer available, and they never made fowler barrels as far as I know, I think you could certainly get a premium for these barrels.

You folks are missing the point on Green Mountain.  Branch Meanley told us when he owned the company, they had 3 lines......2 for smokeless and one dedicated for black powder barrels.  He was and still is a competitor at Friendship.  When he sold the company, they acquired military and private contracts for "black gun" barrels.  In order to keep up with demand and to meet their contract deadlines they put the 3rd line in production making them.  It was purely a financial decision of a company maximizing its resources.  Their monthly production far exceeds the annual production of any current ML barrel maker.

[Joe S]

TOF

I am aware of GM’s history.  They made swamped black powder barrels when it fit their business model, and quit making them when the barrels were no longer a good fit for what they were doing.  That’s business.  But what is profitable for a large business and what is profitable for a small business can be two very different things.

My point is this:  there is a market for “gun barrel steel” barrels (whatever that means).  Some of us would be willing to pay a premium for them.  How much?  Personally, I’d be happy to pay 20-50% over the current cost of a barrel, just for my own peace of mind.   Would anybody else pay that much?  I don’t know, you’d have to ask.  Can a small manufacturer afford to make these barrels at that price point?  I don’t know.  Perhaps one of them will comment.

[JTR]

If the 100 ton minimum order is correct for "gun Barrel" certified steel, I don't see many ML barrel makers jumping on that one. That would be enough for what, 20-30 thousand barrels?

Even if all the ML barrel makers in the country got together for the purchase, I doubt that would pencil out... Then throw in whatever re-tooling that would be required,,, Hmmmm,,, good luck.

It does look like 4150 is available in small amounts, but is that a certified barrel steel?

John

[Scota4570]

TOF

My point is this:  there is a market for “gun barrel steel” barrels (whatever that means).  Some of us would be willing to pay a premium for them.  How much?  Personally, I’d be happy to pay 20-50% over the current cost of a barrel, just for my own peace of mind.   Would anybody else pay that much?  I don’t know, you’d have to ask.  Can a small manufacturer afford to make these barrels at that price point?  I don’t know.  Perhaps one of them will comment.

My cursory research says that a the price of the steel for a barrel, when bought as one unit, is about $25 for 12L14 and $50 for 4140. 

The additional costs of machining would be the bulk of additional costs.  I would speculate that some ML shooters could use button barrels.  Octagon shapes could be bought as such from the mill.  Carbide tools can be used.  The barrel would need to be made with more efficient processes.

Producing a swamped cut rifled barrel by traditional means would certainly be more money but is that always necessary? 

[Carl Young]

Google Scholar will search for legal cases (or journal articles) for those interested in pursuing that inquiry, here is an example: https://scholar.google.com/scholar?hl=en&q=%22barrel+failure%22+%28rifle%7Cshotgun%7Cgun%29&btnG=&as_sdt=6%2C25&oq=barrel

Since there is no standard terminology for the problem, you may want to search using a variety of relevant search terms, i.e. rifle, shotgun, gun, barrel, failure, defect, stress, etc. in multiple combinations. The cases you find will cite other cases which may be pertinent. Legal cases only offer guidance on legal issues, so technical information on barrels or steel will be an indirect concern of the court.

I gently and respectfully ask that if you wish to discuss the legalities of this issue (and I do not), that you start a new thread so as not to dilute the technical discussion in this thread.

Eric, my apologies that this is not directly responsive to your questions. I wish you good luck, as I also research questions that have few, if any, known answers and understand the frustration of wanting more information than is available.

Regards to all,
Carl