Deus Machina
Member
Once a bullet is pressed into the casing, the mouth of the case is pressed to roll (roll crimp, common for revolver rounds and more pronounced) or squeeze (taper crimp, for rounds that space against the case mouth instead of the rim) slightly inward, tightening it against or crimping it into a groove in the bullet. More so on revolver rounds for specifically this reason.How does a round "jump crimp???" Perhaps I should ask what is the "crimp" that was being jumped?
"Jumping crimp" happens when the gun recoils, moving everything--including the casing--back, but the bullet itself tries to stay in place, scooting forward and partially out of the brass.
Jump it far enough to protrude from the cylinder face, and it can't rotate. If it happens in the wrong spot, you can't even open the cylinder.
Congratulations, you just locked up a revolver.
Obviously this happens more to lightweight guns like my Taurus 85 UltraLight, and is rare for weighty, forward-heavy guns like a S&W 586.
It's exceedingly rare for semi-autos, aside from the Bond Arms Bullpup 9, which feeds by pulling a round out the back of the magazine--and can occasionally yank the case right off the bullet.
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