Hi all, my first post here.

Re what happens on firing a double rifle is a bit of a mystery and the explanations do not seem to match experience 100 per cent.

Look up pipe guns etc on youtube and there are clips showing totally unlocked systems holding together during firing. Apparently the friction between a shotgun shell and the "barrel" is strong enough to keep both together during recoil. In one case where the "barrel" mass is too much for the friction bond the cartridge does come out, flinging back the "bolt". This is not to suggest that the same happens in a rifle but it does contradict the long held notion that the cartridge head acts alone on the breech face.

Then there is the emphasis on the lock up and value of multiple locking points. The Chapuis has no central action bridge, ie no fitting on the circle, no top bite of any kind, and experience has shown that it does manage with heavy calibers.The Winchester Model 21 has a simple lockup and it also seems to hold up well.

We have not seen any analysis of the Poisson effect in break open guns. Thick walled cylinders show radial expansion and axial contraction when under pressure. And naturally there is rapid recovery after such an expansion-elongation phase. This might partially explain the results from old tests re the benefits of top fasteners and the flexing of the bar.

Some people have written about how they shot break open shotguns that were unlocked or had the locking bits removed. Assuming the reports were truthful, the fact that these "experiments" did not mention any tendency for the guns to open on firing, show that the forces developing might stress the action in ways different from those assumed.

If only we had some hi-speed film of the action during firing!