Underhammer Round Ball Rifle

[Kenl]

I'm looking for information on an underhammer rifle. It has a 50 caliber 35"x1 5/8" barrel by W.W. Large. the twist is one turn in 48" and is equipped with Redfield Olympic sights and is drilled for a false muzzle, of which I do not have. The hammer trigger assembly is signed B.Sehlin {maybe Selbin} 1967. The half stock is very nicely made of walnut with rosewood grip cap and a diamond inlaid midway on the underside of the forend. This is a really robust rifle in very good condition. any information about the maker, history or value would be greatly appreciated.

Jim could you post a picture of the action?