I'm going to stick my neck way out, now theres something new, and say its Native American built. The general shape looks like a chiefs grade North West gun, if you ignore the odd cheekpiece. The trigger guard, looks like the tang, and the bow, are one piece, and the front of the trigger bow just tabs into the trigger plate. Trigger guards of this type are seen on committee of safety muskets, and barn guns. The conversion to percussion is called a Belgian conversion and is seen on percussion conversions for the civil war.
Hungry Horse