Hey guys and gals I need your help. I have a s&w 340 m&p. I noticed the other day that after shooting a good 75 .357 rounds through it that there was some makings exposing metal on the cylinder. they are very small marks but have a circular mark as if the barrel in someway contacts the cylinder while rotating. I don't have any feeler guages yet but can see light between between the cylinder and barrel. I have ruled out leading on the cylinder because it is a fairly new gun and have shot maybe 10 lead rounds with it. The cylinder face has been cleaned so my question is this. Is it possible that the heat from the magnum rounds expand the barrel enough to touch the cylinder face during firing and later cool down to a normal gap???