Pretty rough shape. Looks like some old military musket parts assembled into a home made stock. Lock plate shows signs that it was once flint. The cone in barrel conversion was one of the common methods used for conversions. Sideplate, sling swivel and trigger guard look like they may be re-used military parts as well. Stock is shaped more like a later shotgun or sporting rifle stock through the wrist and pistol grip area. I would suspect that someone had an old musket, possibly already converted to a hunting gun with a broken stock and they made a new one so they could keep using it. Re-used as many parts as possible and added a little decoration at the breech for their own enjoyment.
As to identification it has been rusted so badly all exterior markings are likely lost to time. If it can be taken apart there may be surviving marks inside the lock or under the barrel to narrow down what it once was. The general shape of the lockplate resembles some early US muskets and the cone in barrel conversion was common on US Arsenal conversions and some state arsenal conversions. So it's possible the lock and barrel were US made. The sideplate looks a little off from a US one so it may be from another similar (foreign made) gun or a home made replacement. An interesting piece of history
