Sorry but I don't know what it is. However, a gunsmith could probably tell you if it could be restored, if restoration would ruin any historic value it may have (some things are better left in original condition), or if it would never be fireable but would be a cool wall hanging.
It is difficult to tell a great deal by the photos. I does appear to have a percussion rifle lock. However, the barrel is not positioned properly for a snail and nipple. The barrel appears to be held to the forearm with some type of twine, leading me to think that that it was a victim of some shoddy repairs. The barrel appears to be too thin for a shotgun. If there are no markings on the gun, it may have been produced by one of many regional makers in the 18th and 19th centuries. Regardless, this gun is definitely in the wall hanger category.
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