Originally Posted by Mark Dozier
In this case a TAMPER crimp and that should solve your issues.
Virtually no .45 Auto die sets come with roll crimp shoulders anymore. They are pretty much all taper crimps now, so I'm sure that's what he's using already. More mouth belling could help, but it also causes case mouths to split sooner if you do too much.
I have to disagree on the M die. I fought the uneven bulge problem relentlessly on my Dillon Square Deal after I first got it. No amount of belling made any difference except with bevel base bullets, and those don't shoot as accurately as plain flat base for me. Dillon, of course, only makes taper crimp dies for auto pistol pistol dies, so that's what I was using.
I wound up grinding an M profile into my Dillon Square Deal's expander/powder measure operating tube. That expander profile stopped the problem almost completely (slight unevenness can occasionally occur, but it's never all on one side anymore) and my .45 Auto bullseye gun LSWC groups shrank about 20% as a result.
I can't say it mattered much to jacketed bullets, though. They tend to be tough enough to straighten out entering the throat at pistol pressures. But lead is sensitive to any degree of bullet misalignment as the bullets tend to swage into the throat at the angle they begin the firing event with. That leads to imbalance due to the resulting mass asymmetry out beyond the muzzle.