Interesting gun. While this is purely a guess, I think the architecture and metal work point to upstate New York. The gun has a similar "look" to work by B.C. Wood of Painted Post, N.Y., who made alot of doubles with one rifled barrel and one smooth barrel, as well as drillings. There were some very innovative makers in that area in the late percussion period, and the unadorned metal work combined with fancy trigger guard were common there. The hammers are particularly reminiscent of that area. Just a thought....I could be way of base.
ELee