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

in "The Gun & Its Development" W W Greene described fitting one of his guns so it could hold a non elastic strip between the breech & barrels. He removed the connection between the top lever & cross bolt & built a bolt with extended length so it could be inserted or removed by hand. With normal loads he reported the trip remained intact with or without the crossbolt. As loads were increased the strip began to be broken when the cross bolt was removed, but remained intact with the bolt in place. In fact he stated he went to some extremely excessive loads but could not break the strip with the cross bolt in place.
It would indeed be interesting if someone who had the facilities to do it wold take a long recoil operated shotgun & remove the bolt which locks the breech-bolt & barrel together.
Then set up & fire it while filming with the high speed photography. The barrel would of course have forces working both ways on it. Friction from the shot & wads would be trying to push it forward, while friction of the case would be pushing backwards. Would be interesting for sure to know which force won

Yes I read that one. Also read the experiments described by Gough Thomas with the ball of plasticine trapped between the barrels and action, and the varnish painted across the barrels and fences.

These experiments do not isolate the effect of radial expansion, axial contraction in the barrels, which might be a causative factor in the plasticine flattening out, the varnish breaking or the tape being snapped.

Explaining the situation by reference only to the action, while ingoring the barrels seems a tad unscientific. Especially when the barrels are of soft tensile steel and the action is chunky hardened and fairly stiff.

I suppose if one tries Hard Enough anything & everything can be discredited. It seems to me though that even if the sidewalls of the case had full adhesion the case head itself would have more rearward expansion than the barrels have radial expansion. Understand I'm not denying that radial expansion exists, but steel is stronger than brass. I simply do not think that it can be denied that a back thrust is applied to the breech/bolt of a gun. Simply too much evidence of it to throw it all out. As noted radial expansion doe not account for a blowback mechanism operating, Back Thrust does.

Naturally there is rearward pressure and no discredit is intended to anyone. What is not being analysed are the phenomena that occur simultaneously with the rearward thrust.

On firing the case expands and sticks to the walls of the chamber. Does the backthrust then come simply from the case head or the case head plus the barrels?

During this phase the chamber expands radially, it also contracts axially.

The action flexes.

And then there is a recovery phase.

The action flexes back to its rest position as do the barrels. So far I have not come across any authority mentioning the recovery of the action from flexing and whether that recovery delivers a blow to the chamber ends of the barrels, especially if the barrels are also recovering from their axial contraction at the same time. Could this be the cause of the swarf raised on the chamber ends of some barrels? Or the burnished hammered look on some chamber ends and the marks made by soft barrels on hardened breech faces?

The pressures applied by the action recovering from its flex must be considerable. Does this slam the barrels between breech face and cross pin hard enough to alter them dimensionally and put them off face?

These are valid questions that the traditional descriptions of the initial back thrust phase, and nothing else, do not answer. Considering the drop in popularity of SXSs they will probably never be answered and they are more relevant to repair than construction of new guns.