Originally Posted by
MountainDevil54
there wont be pressure once the firing pin is adjusted. The primer on the left gets like that due to it being blow back, basically launched like a projectile............
That's not true. The primer on the left is the same length after being popped as the one on the right. They both were popped in rifle-breech plug combinations that controlled the expansion of the anvil out of the cup. The primer on the left wasn't launched like a projectile. It was contained in a zero slop headspace environment.
Actually the one on the left was used to fire less powder than the one on the right.