"... near the top ..."
Near the case mouth?
By upper chamber, I assume you mean the top of the chamber mouth? How do you know that?
"... all rounds chambered and fired OK without malfunction. ..." If they all fired, then the dent is probably related to ejection, not chambering, don't you think ...? Firing cycle pressure usually irons out dents and dings in the case walls.
If the rounds are tipping up too far during the transition from magazine to chamber, maybe you could run the bullet out a little farther (don't seat quite so deep) to give it more front weight.
[This message has been edited by sensop (edited June 18, 2000).]