doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com THAT was close

The measurements in Drew's picture don't look like "blow-up" thicknesses. Back to the obstruction theory.

So tell me, Doc. If it doesn't stretch "much", where does the extra steel come from that goes into creating the big bulge? Be specific, please.

Measure the thickness of an uninflated balloon's wall, then measure it after it is inflated. What do you think the results will be?

"Not much" in one's man's vernacular may well be enough to cause a rupture, in another's.

People shoot old ammo or load ammo to low pressures, therefore, obstruction should not be ruled out.
I have simple rule if 12ga gun can't handle 1oz game load at about 1250fps or 7/8oz for 20ga I dont want to own it or to use it.
Classic guns are cheap now. Last one I looked at was keeper gun from Birmingham by English & Son (very prestigious shop from Bath Street). It had 28" imp cyl-mod barrels 2&3/4" chambers with 1&1/4oz proof, $500 plus tax.

Stan, you are right of course. "Not much" is a very relative and subjective term. And we have to remember that steel is a collective term for many different alloys that have very different properties. When met labs do tensile strength testing, they machine the samples down to a precise cross-sectional area, and then they are clamped in a machine that pulls them apart. This UTM Tester simultaneously measures the elongation and the amount of force used to stretch the sample to the point of failure. They are able to determine the yield strength, or point where the sample can no longer spring back without suffering permanent deformation. The Ultimate Tensile Strength is the point where "necking"or thinning of the sample occurs before it fails and breaks. Some structural steels can elongate around 30% before pulling apart under tensile strain. So-called mild steels may elongate 15-25% before breaking. Tool steels or alloys more subject to brittle fracture stretch much less before failure, but of course, such steels would not be used for gun barrels.

That isn't a lot compared to much more ductile metals like soft copper or gold, but there is indeed some thinning. I've personally seen many samples and seen tensile strength testing done, and this thinning or "necking" at the point of failure is visibly evident.

The failure of the Flues barrel above is very similar to that of two 20 ga. Flues parts gun I have. They also have very thin barrel walls at the point of the split, but were further back along the forend. Just as there are different grades of steel, there are different degrees of barrel obstructions that may lead to a burst. A lighter obstruction such as snow or a stuck wad might not cause the characteristic or distinct ring bulge that might come from a heavier bore obstruction such as mud or ice. This Flues was probably fired many hundreds or thousands of times before the barrel split, so the thin barrels alone probably were not the cause. Without knowing the particular details involved, all we have is conjecture.

True for shotguns.
Not so true for rifles, where it also happens (Sako comes to mind...).

Previous thread. I'll work on getting the images restored if I can edit.
https://doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=563636&page=3
The Winchester barrel wall thicknesses just before AND just after the burst were .044". The thinnest part of the bulge was .038".
The amount of thinning is likely primarily related to yield strength and the point of the obstruction ie how thick the barrel was to start with. This is an obstruction at the forcing cone



Elastic limit comparing damascus and fluid steel



I asked the metallurgical engineer at METL how much barrels thinned as they bulged. He looked at me like "the formula is too deep for you" and said "not much".
I didn't argue with him Stan.
I'll dig out my barrel evaluations that document wall thickness before, after and at the bulge and post them.
To repeat. I took Statistics as a M1 in 1974 and understand a sample size of one does not create statistical significance. That does not mean however that the results have NO significance.
Anyone willing to invest the time, effort and money to add to the sample size is most free to do so.

The previous thread regarding the image posted and wall thickness measurements, and opinions varied. It was an abused and old gun using ammo of unknown pressures known to have squib loads
https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=13496&page=1

Almost surely an obstruction with a ring bulge and rib lifting



Almost surely related to thin barrels, honed to .018". I don't know the ammo used



I've posted this before. MX2000 honed to .012". That is not a ring bulge.

I've always learned best with pictures. An Armor steel tensile test
Yield was at 57,500 psi (when the sample first began to stretch past .2%). It stretched 12.3% before breaking = Ultimate strength at 101,700 psi.