People fixate on the 48" twist, but that is really not the issue. Many very accurate round ball rifles have been built with a 48" twist. The problem is that T/C and the Italian or Spanish clones have very shallow grooves, only .004"-.005" deep, whereas real roundball barrels run .010"-.014" groove depth. It is the commonly used shallow grooves which have given the bad rep to the 48" twist. T/Cs with a 66" twist are not noticable better because they still have .005" groove depth since that is about as deep as can be done with button rifling. I believe they did do some cut rifled barrels for limited runs but the standard gun everyone shoots is button rifled .005" deep regardless of the twist rate.