The lock is an obvious reconversion, and the gun was used as a percussion at some point. Hard to tell from the pictures if there's an original notch in the wood for a flint hammer or not. Given the wrist repair, strange at best, makes me wonder if the back part is original to the front part! In hand, you could tell if the wood grain matches front and back, but not in the pictures. At least I can't.
But the butt, and up to the lock area, looks like possibly a gun by Whitson. Well bought if both pieces are original to one another!
John