Mystery may have been solved
This could be a North Star West version of the North West Trade Gun.
It had the Sitting Fox Stamped or cast into the lock face.
Originated by Curly Gustomski in Dayton Ohio in the 60's it was later sold and moved to Glecoe CA. and then to Superior, Montana and again to Frenchtown MT. in 2002.
It is no longer in business but made pretty authentic reproductions of these Trade Guns for many years
Check out Museum of the Fur Trade in Chadron, Nebraska. for details on originals.