doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Why doesn't this barrel blow up?

I don't think there is any disagreement between my statement and yours, Miller. Certainly there is back thrust when a shell fires. What I think I failed to state was the difference between thinking that the shell itself, and alone, moves rearward against the breech. It moves, but with the barrel.

Thanks, as always, for your clear and understandable way of explaining the principles at work.

SRH

Stan;
have been away from home a day or so & had limited time on-line. I was not disagreeing with what you said. I am strongly disagreeing with being able to fire a shell totally unsupported & have it stay in the chamber without moving back.
On a gun with barrel threaded into the frame or receiver if this were the case there one would be no need for a lock on the bolt, other than enough to keep it closed until firing. There would be absolutely no concern of bolting strength regardless of type, trapdoor, toggle joint rear bolting etc, all would be equal. I think we virtually all know this is simply not the case, whether shotgun, rifle or pistol.

2-Piper,

No one is suggesting that bolting is unnecessary. What is evident in these videos, done by arguably foolhardy folks, is that there is an obvious friction element that causes momentary adhesion of cartridge case to chamber. At least that was my take when I saw the clip of the Mossberg barrel recoiling backwards after the detonation of the unsupported cartridge using a BB gun as a firing pin.

The cartridge case did not come flying out of the barrel. Rather the barrel and cartridge flew back together with enough force to upset a bunch of logs tied on as ballast.

Seeing that event I wondered if that is not how the barrel ends leave their mark on the breech face of break-open shotguns. The "auhorities" say that the marks are made by the breech recovering from flexing back after receiving the "hammer blow" from the cartridge head.

I do recall that in the early days of blow back actions grooves were cut in the chamber to prevent case sticking and failing to push back the slide.

Here is the video- https://youtu.be/VqQ4ff2VqZY

Well certainly there is some amount of friction holding the case in the barrel. I'm afraid this test doesn't really prove a whole lot though. Some force is obviously going to be lost when the primer blows & pressure is vented out. A battery cup shotshell primer leaves a rather large vent hole. The BB gun was set so close that an indent of its muzzle was imprinted on the shell's base. Who can say if it had not been there if the shell would have been totally blown from the gun or not. As soon as the primer blew pressure fell & burning was not complete. Also what would have occurred had the barrel been more firmly fixed rather than being able to rock so easily on that rather small stick of wood.

I do recall guns having fluted chambers, but don't recall they were the "First Blowbacks". Several companies were making pocket auto pistols on the blowback principal more than a century ago & I don't recall any of them having other than a standard chamber & the chamber did not need lubrication for them to work. The higher pressured 9mm largo was made to work as a blowback design in the Astra 400 by use of a very heavy bolt & strong recoil spring, so obviously a good bit of back thrust there. The .45ACP worked by blowback in the "Tommy gun" also by use of a heavy bolt.

I also recall rifle pressures being measured by measuring back thrust while using oiled cases to cut the friction. Apparently they gave reasonable accuracy, though I am certain they would give a different reading than a modern Piezoelectric sensor.

Note the behavior of the device on recoil when held in the hands, without the benefit of a stock to act as a brake against the shoulder.

https://youtu.be/VcnLja_DuwM

And here is one where the breech flies off, due to its low mass, per the designer.

https://youtu.be/MbcMwPdoEd0

Interesting that the amateur job in the first video did not lose its breech even though it does not appear to be of much greater mass.

The blow forward action-

https://youtu.be/YKo06FgXlMM

Interesting to ponder how this phenomenon affects a break open shotgun action.

In the first video for all except the last shot he had the breech against a tree, so obviously it wasn't going anywhere. Without data as to the actual weight of the two breech sections its impossible to determine why one Flew Away & the other didn't. The one which did makes it obvious there is indeed casehead thrust.
On the blow forward action the case head was supported by a solid breech with the bullet entering the barrel pushing it forward.
As the gun was able to operate & the extractor stipped the case free it would seem this conclusively proves the case adhesion was not equal to the force applied to it. Had it been it would have simply acted as a single shot.

sure, there is missing data, as to the mass as well as the surface finish of the "chamber" walls of both contraptions.

The phenomena cast doubt on the traditional explanation that the only thing happening in a break open action is flexing the action body due to cartridge head backthrust alone. Ignoring phenomena such as thick wall radial expansion and recovery, basing the explanation solely on what is convenient does not seem to cover the situation.

On some of those SXS's that were tested with increasingly heavy loads until the barrels failed, the frames began to show bending and such due to backthrust from the heavy loads one or two firings before the barrels finally ruptured.

One test was done on a rotary bolted L C Smith which had the chambers opened to take 3�" shells. Testing began with full power loads & went up from there. Testing halted prior to a burst when the gun began consistently opening itself. This would be a result of the barrels & breech being Sprung Apart. I believe it would truly be irrational to think this was the result of the barrels being shoved forward, rather than the breech being pushed backwards.

I have always wondered if the spring back and recovery of the frame was sufficient to imprint the shapes of the muzzle on the hardened breech face. From the videos of the contraptions it looks like the cartridge and barrel might in fact be travelling back together and pushing the breech face in unison, hence the imprints of the barrels on the breech face. And if that happens the total thrust on the breech face might be greater than that generated by the cartridge head alone. Such thoughts arise when seeing these primitive things being used.

I wish we could convince some of the high speed video people to film SXS and OU actions on firing. To see what in fact happens.