2-piper,
Interesting point about blowback actions. But if you recall one of the problems in blowback actions was case sticking, and one of the ways invented to overcome it was the grooving of the chamber which allowed gases to surround the case and thus equalise external and internal pressures.
The blowback cycle starts once the inertia of the bolt has been overcome and by that time the bullet has left the barrel, pressures are at about zero. I suspect the same would happen in an Auto 5 without bolting if the chamber is not polished slick.
An interesting point about zipguns is that they keep together as long as the "barrel" mass is such that it does not overpower the frictional grip of the case on the "chamber" walls. When a heavy "barrel" is used then the "bolt" pipe does fly back smartly. This much is viewable on Youtube.
I am not advocating the manufacture or use of these abominations. But their behavior gives some interesting clues about what happens when a shotgun is fired.
American made shotguns are not weak, I did not mean to imply this, I did not express myself well in that post. On the contrary, they are plenty strong. However to the European conditioned shotgunner the single top bite seems weak. We Europeans assume that the only proper bolting for a SXS is via unerbolts, possibly aided by a top extension.
The simple practical top bite is not the only area where US makers pioneered new and possibly better ways to do things. The Lefever ball joint is a brilliant example of design foresight. It avoids all that messing about when it comes to tightening a loose shotgun. Amazing that it was not copied, but perhaps not, European makers tend to suffer from "mental inertia" as Gough Thomas pointed out.
