It appears to be a Howdah pistol, and could have been made either in the US, or more likely Europe, with Belgium being most likely. It isn't a pinfire piece, as the hammer hits the rear, and not on top of the barrel.
Look closely for any markings, and take close up photos, especially anything that looks like a proofmark (usually on the underside of the barrel).
Google Howdah Pistol, and there are a couple of decent reads.