Stan has some interesting observations regarding the friction component of the shell in the chamber.
Considering the obvious markings of the barrel walls on the standing breech of some shotguns, I would say they are evidence that barrels and breech meet with enough force to make those imprints. Is it because the barrels thrust back, or the breech springs forward from the flexing?
Re the blowback force. Some auto pistols used a blow forward action. They can be seen in videos posted by the forgotten weapons people on youtube. Another one of those perplexing things about firearms.
And lastly there is that video of the open Mossberg barrel recoiling together with the shell. Fascinating footage. The shell has not thrust back from the chamber even though there is no bolt to hold it in. The barrel and shell recoil together.
Obviously these phenomena contradict the gospel. A closer, more scientific look might be worth doing, and might explain why break open designs shoot loose. The cause could turn out to be something unexpected.
