I figured it out. The root cause is that I'm stupid.
I didn't realize the rcbs seating die was putting a crimp on as well as seating the bullet. I backed the die out and all is well.
So I'm trying to reload some 454 for the first time. I have the RCBS carbide set of dies and some new Starline brass. I'm having a serious problem getting the bullets to seat in the case. They start easy enough, but then they get really tight. You can see from the picture what happens if I...