Did you ever figure this one out? If not, what press are you using?
I had the same issue with my .45 dies in a Lee Deluxe Turret. Finally figured out that the turret head was just ever so slightly out of timing. The plastic ratchet on the index bar had worn. Replaced that ratchet and things were smooth from then on. So die alignment with your shell holder could be an issue.
This was happening with my Lee seating die, that was not set to crimp.
LC
I had the same issue with my .45 dies in a Lee Deluxe Turret. Finally figured out that the turret head was just ever so slightly out of timing. The plastic ratchet on the index bar had worn. Replaced that ratchet and things were smooth from then on. So die alignment with your shell holder could be an issue.
This was happening with my Lee seating die, that was not set to crimp.
LC