I reload for a number of different calibers, most of which use a taper crimp. I do understand the difference between a roll and taper crimp. My question is, as the title asks, HOW does a die roll crimp? The diameter of the bullet is larger than the cannelure depth. It would seem that it could not push the case mouth into the cannelure with out shaving off the upper portion of the bullet. What am I missing?