Mark, since you stated an "iron on mounted mountain rifle" I would concur with Dennis that the best evidence, guess work and gut feelings aside, is most of them were browned, especially after 1800. Charles Sawyer in one of the early histories of American Rifles, states the mountain gunsmiths used a sal ammoniac browned finish. Angier sites that reference and I looked it up once, Sawyer wrote i t in the late 19th century. Hacker Martin was also a firm believer in rust browned barrels on iron mounted guns. The lock is anybody's guess. I usually brown mine on the exterior, because you can't really heat blue it and I don't care for case hardening. I boil the locks however so they come up almost black. The iron mounted rifle I posted a couple of months back has that finish approach.
My original Jaeger has a rust blued lock and the barrel is hard to tell, maybe charcoal maybe rust blue.