RE: "I have this old gun..."
jaybe
Do not and I repeat do not refinnish the gun !! By refinnishing it ,you can devalue it a great deal. Also do not refinnish the wood.
You should find some small proof marks on the barrel neer the breach ,possibly on the under side. These will help you identify what you have there. There is also a book out that values old BP guns , but I don't recall the name. It may be one of the GUN TRADER books.