How much clearance is recommended between the stock and barrel? I want to make sure I have enough so as not to cause problems with heat/harmonics. I have one with about 1/8 inch, several that a dollar bill will easily slide the length of the barrel, and a couple that are much tighter than that. All shoot fine ecxept one of the really tight ones. I haven't figured out if its interference or the load. Wanted to rule out any interference first.