ok, total rookie here so if im asking a dumb question go ahead & drop the piano out the window right on my head ... friend & i tried to swap buttstocks & failed ... mine is a ROGGIO lower w TAPCO 6-position collapsible ... his is a bushmaster fixed(A1?A2?) ... here we go : tapco came off the roggio lower just fine ... bushmaster came off just fine after considerable torque was applied to break loose... all good ... the tapco then screwed smoothly into bushmaster lower A-OK ... however the bushmaster buffer tube would only go about 1/2 of a thread into roggio lower before getting REAL tight & not "feeling" right ... we stopped before buggering up threads on either piece & aborted the project much to both of our disappointments ... any ideas what we ran into ?