I slugged the barrels on the two Mosin Nagant rifles I own. A 91/30 and a M44. The M44 slugged out to be .314 no problems. The 91/30 slugged out to .3145. The problem is that after I got 3 or so inches down the bore the slug started to feel loose. I could move it down the barrel without the hammer. When I got close to the chamber it tightened up again. I can get 4" groups with Czech silver tip at 100 yards. What is the reason for the bore opening up a little halfway down? What kind of issues will I run into shooting cast boolets. I am looking at montanabulletworks.com .311-.314 Linotype gas checked bullets. Thanks for the help.