I tried seating Barnes X bullets .050" from the riffling, and did not obtain great accuracy using .30 cal. 180 gr., and 200 gr. bullets. I set the bullets .010" from the rifling and received groups under .75" groups. I have had the same experence with .270 cal., 7mm cal., and .338 cal. I believe the use the .050" measurement isdue to saftey percautions, but if one works up the load slowly there should be no problem. Good luck.