Recently purchased a 30 cal 308 McGowen barrel on line. I have been having trouble making it shoot the way I want, 600 yards. Had a chamber cast made and found that the chamber neck was 0.348" and my loaded round is 0.333". Other than over working my brass do you, as I do, think this is effecting my load development. I have my own answers just want some other feedback. My turned case necks are 0.012 Thanks