I wonder if an improperly machined shell holder couldn't also be causing the problem? Maybe it is "presenting" the case slightly off angle?
That's an intriguing thought, but I'm using the same shellholder I use with my .30-06 dies. It's the Redding Competition +.010, and incidentally I used most of the rest of the set with the .30-06, trying to size cases from my old Mark X small enough to work in my NULA. (Can't be done, it turns out.) Anyway, all of those worked fine.
