Could that be a Hawken Shop gun?
Will be interesting to see what they say! Just curious, what does it weigh?That's been my thinking. There was a printed page from their website in the shooting bag that accompanied the rifle. There's a serial number hidden on the bottom flat. I'll have to call them up and see if they have a record of it.
Yours looks very similar to mine that I built from a Green River kit back in the early '80s. My barrel is also a 1:48 twist, but the barrel is only marked ".54". "J&S Hawken" is stamped on the side of the lock.
i use a traditions build it yourself and nice elk and sheep