BSR, I keep coming back to this gun and think Charles Slotterbek either was in close contact with the builder of your gun, or one of these gunsmiths trained the other. My C. Slotterbek has the same barrel treatment as your rifle, including the turned muzzle for a bullet starter, no underrib for the ramrod pipes, and I would suspect that the forearm barrel key on you gun passes through a slot in the bottom of the barrel. C. Slotterbek also used the same triggerguard except in steel instead of brass.
I meant to ask you if your gun has a cheekpiece, those built by Slotterbek after he moved from San Francisco to Lakeport do not.
Hungry Horse