Originally Posted by
Herbmiester
I think Spanners is on the right track. I suspect your chamber is on the tighter side of the acceptable tolerance and as such your die is not sizing the brass far enough around the base area. If the brass chambers with a ground down shell holder this could be because you have resized your base slightly or it could mean you have reduced the length to the datum of the shoulder. Personally I suspect that its a base size issue. I have a DPMS AR10 and I use a Forster FL die and have no issues feeding and extracting unfired rounds. I think trying a Small Base die is worthwhile, I use one exclusively in my AR15 and it does not seem to have affected accuracy, and it guarantees no matter what brass I put through what gun it always chambers and extracts.
In the past I have noticed Lee dies do not resize the base as much as some other brands like Redding so swaping dies with a mate may be worthwhile. Oh was the brass that is a tight fit in the shell holder fired in the DPMS or another rifle?