I got a bush basket of 308 brass - military. I had similar problems. I bought a small base die. Still same problems. I talked to a RCBS technician. He told me to set the full length sizing die 1/4 turn past touching the shell holder. That did the trick. I didn't have to resize that way after that. Evidently the brass was shot with a M60. The base was too wide.

I prefer classic.
Semper Fi
I used to run with the hare. Now I'm envious of the tortoise and I do my own stunts but rarely intentionally