Needless to say a barrel could have been replaced at a weapons repair station in country or it could have been replaced last week. It is also very possible during the rebuild that the carbine went through (as just about all did) that it was replaced then, again maybe the IBM had a bad receiver and the Winchester a bad barrel. On the stock in on the barrel channel edge there could be the letters SA. Springfield only marked their stocks there. Springfield sight is a replacement, again probably done during the rebuild/upgrade. Stocks can be changed as easliy as you change shirts, so who knows how long it has been on the weapon.