I'm a newbie, help!!! What is a "roll crimp" and what is a "taper crimp"? When should one be used rather than the other?

This will not be a "textbook" answer, it will just be my attempt to explain the difference...

A roll crimp is typically used to crimp a handgun bullet in the part of the bullet called the "crimp groove". It is the tapered area just behind the driving band on a semi-wadcutter bullet, and it typically is somewhere around .075" deep and maybe 1/8" long. Most often, roll crimps are used in revolvers, but not exclusively. They are also used by some reloaders to crimp rifle bullets, and in this case the crimp is placed in the bullet's cannelure.

Taper crimps are most often used in semi-automatic pistols. This crimp is typically used on bullets without a defined crimp groove, like most semi-automatic projectiles. The bullet is seated into the case down to where overall cartridge length is within specs, and then the mouth of the case is taper crimped into the bullet at a point on the projectile where the bullet is at full diameter, below where it starts to narrow and transition to the nose, or point.

But again, nothing is absolute... One can taper crimp a semiwadcutter bullet into a revolver case. In this application, the crimp would be placed somewhere on the driving band, typically, since that is where the full diameter of the bullet is.

And finally, you usually use a taper crimp on cartridges that headspace on the mouth of the case, i.e., rimless cartridges like the 9mm, 45 ACP, etc. Roll crimps are used mostly on rimmed handgun cases, which headspace on the rim.

Roll crimp






taper crimp



The roll crimp into a canalure makes a more positive connection so that recoil can't yank the bullet out and jam the revolver.

But the semi auto pistols most often headspace on the case mouth, so they can't have a roll crimp. The best they can get is a taper crimp.