This rifle has the all the appearances of being a rifle that was custome built. The workmanship is pretty good on it. Many original locks were marked warranteed - this lock looks new - by that, I mean it is not an antique. The rifle may have some original parts on it. If it was purchased in the 70s, my guess would be that it may have been made anywhere from the 30s to that time. It appears that it had captured barrel keys on it - the hammer may be an original but the lockplate just looks too "good" on it. As I said, it looks like good workmanship on it and if the bore is good, it looks like it would be a good shooter. When I began shooting BP in the 60s, there were a number of lockmakers, barrel makers, etc. that advertised in Muzzle Blasts - the NMLRA publication - that are not around today. As suggested, pull the barrel and see if there are any markings on any of the floats or on the breech end. There were a number of barrel makers in the 60s - Bill Large was well known as wee others. I might be proven wrong and it wouldn't be the first time - but I'm still guessing that this was a custom made piece - possibly with some original parts. Even if it ends up nnot being an "antique" - it's a great looking rifle. Let us know if you find anymore out about it or if there are any other markings.