The lockplate and bolster indicate that it is a British Enfield, probably an Model 1853, or a reproduciton thereof. Unless someone can decipher the barrel markings, don't know what other information would be available.
It was probably a rifle musket originally, then maybe converted to a shotgun. The wire wrapping in lieu of a band is obviously not original.
The modern musket nipple does indicate that some recent owner wanted to fire the old gun, but I would hesitate to do so due to its present condition.