I spoke with an RCBS tech, because I was having the same bulge problem with about 5% of my reloads. He said that the crimp we see on factory ammo is actually way overcrimped, and to back off on my seat/crimp die, till I could just barely see the crimp. That sez he, is a proper medium crimp! I mostly seat and crimp in separate operations.
For cast semiwadcutters, I adjust the overall length so the case mouth leaves no gap between it and the top crimping groove, then adjust the seater so the case mouth is just flush with the outside diameter of the bullet, leaving no lip to hang up, and a minimum place for dirt and other nasties to enter. Cured most of the problem, although due to differing case lengths, (I hate trimmming cases!) I use my Lee Factory Crimp Die every so often. Solves the problem handily.
On plated bullets, I lightly chamfer the case mouths, then I use my Dillon seater, which does both a taper and roll crimp, and use very little crimp or taper...just enough to move the case mouth against the bullet so I don't cut the plating.
Jacketed, I crimp lightly into the cannelure,and don't worry about OAL. I've never had a problem with "bullet pulling". (YET!
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