The gun by itself would likely have little or no value. But that is where research starts, not where it ends. Who lived in that area? Was there a battle fought in that vicinity and could that gun have been used in it? Are there any markings on the gun other than the normal ones, like the name or initials of an owner?
The answers to questions like that could mean the difference between a rusty piece of junk and a piece of local history, worthy of a place in a museum.