Personally, I don't believe it's possible to shoot a lead conical without leaving at least some trace of lead in the bore. The more they're shot without cleaning out the residue the greater the build up. Also, the higher the velocity the more build up. A bore button will prevent melting of the base of the bullet and reduce it, but that lead (even lubed) is rubbing against steel. It just has to leave something behind. A lot of supposedly "shot out" TC sidelock barrels turn out to be just fine after getting years of lead build-up from shooting maxi-balls out of the grooves.