I have a question about the bbl markings on older M1As. I recently aquired a used M1A (basic model w/black synthetic stock) serial # 71,040'ish' range, green & white box, made in 1992 . The bbl is marked "308", there is an engraved star, and there are 3 or 4letters; a "R" followed by what looks like a "T" then an "E" or "LF". Please can anyone provide some insight ? I cant post pics yet, but will try later. Thanks for any info. I tried to look this up but no luck. Thanks. Dan