I am having my XP100 in 7br rebarreled. I am playing with the new barrel to see if my loaded cast rounds will chamber and they will not. The new barrel has a .310 neck. If I use the M Die to flare the mouth, the dies will only iron out the flare to .311 and the rounds will not chamber completely. If I don't flare with the M Die, I scrape lead. Any suggestions?