I am wondering what are the key things to look for in determining if some one has a true military version M-14 sniper rifle. I have been reading everything I can find on here and other sources about the different variants of the XM-21,M-21 rifles. I was wondering what everyone on here could tell me to look for. Heel stampings, proof marks, barrels, scopes, manufactures, weather they were full auto or semi, with the stud locks. Did Spring Field Armory Inc. make any? Where they all made from NM unlined barrels? Where they all manufactured by Win,HTR,TRW? Which ones are more collectable and what parts make them that way?