Holy crap dude!When forming your brass, jam the bullet if possible. My chamber is 8 thou deeper than the shoulder on lapua brass. Half my cases aren't blowing forward, and come out of the chamber very smokey. The othe half has fired forward correctly. So I've got to form another 24 pieces, some actually shrunk a few thou fn weird, never had that happen before. My charge weight may be too low as well. I backed off Cuz the first 3 rounds had pressure signs ar 55gr and suspect it was the 2 thou neck clearance of unturned brass. What a pita. It's still shooting moa groups or less while forming which is bizarre, even with all this crap going on.
Sounds like your chamber is all out of spec, that sucks.
I had some Peterson brass that was out of spec on a 338.
I had. 002 neck clearance and was getting pressure signs, turning to .005 clearance fixed it