Both of my early-'70s vintage 40X rifles are marked on the barrel, right in front of the left side of the receiver, "7.62 NATO," with an emblem that looks like an inverted "V" with three points across the top, aka, the heart. On one, it is before the 7.62 marking, on the other, it is after. On the opposite side of the barrel is a three letter code for the date of manufacture. If the rifle is an original .308, the top of the receiver will be clip-slotted. From what I have read, this was only ever done on the .308 repeaters. The barrels on mine are not marked above the stock line with anything else.