Hi group. I am new to Colt Thompson's though I have covetted a Thompson since I went to my eighth grade Washington D.C. trip and saw an FBI agent demonstrate one; unfortunately, being from NJ, i never thought I could own one and always were told they were very expensive. Having moved to Virginia in 2002 (I wish i knew they were only 5k back then), I didn't pursue it. Anyway, I have a savage barrel, (had a 2nd gen cutts compensator on it) marked "S" and wanted to make sure that the barrel that I am comparing it to is a Colt barrel. The "colt" barrel has a mark to line up on the top receiver and has not other markings; i didn't know if my "colt" barrel has rounded enough edges or if the fins were the correct thickness (i read these got smaller as the serial numbers go up?). Were the "lines" only on Colt barrels and receivers? Thanks and correct me if I have made any mistakes.