+1 on this , . 252" or .253" , and .020" freebore , if you're shooting 60g and above .fdshuster said:My PTG 223 reamer was cut with a .253" chamber neck diameter, specifically for Lapua brass. It was an excellent choice. My Lapua brass has 15 to 18 loadings & I've never tossed one because of a split in the case neck.