This.
Your dies may be set up 'correctly', but not quite correctly for your particular rifle, which, by the sounds of it, may have a chamber that is on the short side of spec. You may well have a set of dies that are on the long side, to boot.
Go for the cheap fix first. Spin the dies down a bit, and if that works, maybe trim a wee bit off the bottom of your dies or try a new sizing die.
If it only affects the one batch of brass, not another, maybe looking at the brass, instead of the rifle, is in order. Case necks and shoulders been annealed? If they are to soft, they could be getting pulled forward, if too hard (ie: need to be annealed) they may well be springing forward.
Not to tell you not to spend a bunch of money or anything, but I'd start with the simple fixes and checks first. If the rifle was working well before, and not now, the chamber is likely not your problem.
I'd start with one or two of the offending batch of brass, paint them up with a magic marker, and try to chamber them to see where the contact is, that's hanging it up. Then paint up a couple more and size them, to see where the contact is, and to see if the shoulder is being hit. Then try an anneal, on a couple. Then try a different die, if you are not getting any changes.
Cheers
Trev
