I have always wondered if the spring back and recovery of the frame was sufficient to imprint the shapes of the muzzle on the hardened breech face. From the videos of the contraptions it looks like the cartridge and barrel might in fact be travelling back together and pushing the breech face in unison, hence the imprints of the barrels on the breech face. And if that happens the total thrust on the breech face might be greater than that generated by the cartridge head alone. Such thoughts arise when seeing these primitive things being used.
I wish we could convince some of the high speed video people to film SXS and OU actions on firing. To see what in fact happens.
