I'm unable to provide an extensive answer for you. The forum will time me out and disconnect. However, the following may benefit you.
Three reasons a cartridge won't chamber -
Brass work hardens with age and sizing. It will influence the sizing process. Annealing reverses the hardening effect, and should be performed periodically, although I don't think it is influencing what you are recognizing since the brass chambers w/o problem. Here is a link on annealing:
June, 96 Cases
You probably don't have a problem, as you will come to realize. For brevity's sake, I will let others address the issue.