I load 44 mag for a desert eagle and 2 revolvers. I experimented with both the taper and roll crimps. The taper crimp is for bullets with no cannelure (Groove). The roll crimp is for bullets WITH the cannelure. The powders I use require a firm crimp to work correctly, I use W296, H110 & AA#9. The roll crimp rolls the case edge into the cannelure. The taper crimp squeezes the case against the bullet. Trying to taper crimp to firmly can distort or damage the bullet jacket, also case length variations cause inconsistant crimps. The main goal when crimping is uniformity, it takes practice. Both crimps seem to work equally well for me as long as in each batch the crimp is as close to the same as possible. Hope this helps, good luck.

Gringo Hunter