I am going to look at a Vietnam era M40 this weekend. The rifle has a six digit sn in the 186 range. From the pictures I have it has the REP proof, heart and triangle barrel markings. The barrel is also coded U W N 41 which would put it August of 66 build date. The rifle is parkerized, the bolt is black oxide and is electropenciled on the bottom with the rifle SN. The stock looks to be correct with the black aluminum bottom metal. Currently it has a satin black 2nd gen Redfield accu-trac that has a serial # that begins with Y. Base is 2nd gen with SN stamped on the left front. The sling is leather and marked MRT 1970. Is there anyway to tell for absolute sure if the rifle is real? I know some takeoff parts made it out and were installed on rifles. This one seems to match but I would like to know if there is anything that would be a dead giveaway that the rifle was built up from spare parts. Sorry this post is so long but I don't want to dump a pile of cash on a bogus rifle. Thanks.