Maybe you should have just cleaned the factory grease out,and not used JB? Anyways if you want a tighter fit try the MMP-HPH12 here's MMP web site http://www.mmpsabots.com/ The black sabot that came with your TC XTP mags i think are the MMP HPH24.I hear alot about TC having Tight bores but mine is not Tight ,Like yours.I Didnt use JB,Just cleaned it real good before i shot it. IMO i think TC went to a little bigger bore size in their new rifles.Cause mine and my friends loads anything,heck i dont even have to swab between shots using T7.