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
