Not much to say other than a Hawken style percussion rifle, your not giving enough info about the rifle. Are there any maker's marks or initials anywhere on the barrel?. You would need to disassemble the rifle and look at all the parts for anything that might give a clue to the age/history of the rifle. What is the story from your family, even though some stories get stretched a bit with time and memory. Rifle makers were everywhere, every community had blacksmiths who would have made rifles also. Maybe check with the blackpowder reenactors crowd, maybe they could identify some regional characteristics that could narrow the search.