Hi shotgunlover,

You raise some good examples but you are talking shotgun shells which have straight/parrallel sides with no taper. When you fire the shell the pressure expands the catridge and the straight sides grip the chamber walls. I would suggest if you oiled the shotgun cartridge before you loaded and fired it you might see a different result.

I have seen similar discussion where tests were carried out on rifle cartridges fired from an open barrel. No bolt or breech face to stop the cartridge moving backwards when fired. The straight / parrallel sided cases remained in the chamber when fired, as in your examples above. The cartridges with tapered sides (most rifle cartridges) shot out the back of the barrel as fast as the bullet shot out the front of the barrel.

Food for thought.

Cheers
Rhodes