Problem #1 - If you are not doing this already, ...
- Unscrew the seating stem many, many turns (waaaay out)
- Now screw the die body down until it hits a sized/unloaded case that's all the way up on the ram
- Unscrew the die to get it way off that case at least 1/2 - 3/4 turn. Lock it.
- NOW screw the seating stem down to get the proper OAL.
This way there is no possibility of inadvertently crimping while the bullet is still moving into
the case--and thereby crushing the shoulder a scoch.
Problem #2 - a Bolt face that is not perfectly square to the case head can/will shave "flecks" of brass.
Not unusual, but that's not keeping the bolt from closing. That sounds like headspace.
Problem #3 - Are you full length resizing? ... Sizing die all the way down to contact
the ram/case-holder, and then 1/16 turn more to overcome any flexing in the press?