[Jim K]

I think it is a converted military rifle, though I can't put a finger on the exact model.

In any case, please do not even consider spending time and money trying to restore the old gun. It is very likely that it could be dangerous if fired with any modern ammunition. I would keep it as a wall hanger, and limit work on it to cleaning off the worst of the dirt and rust and applying some oil.

Just FWIW, the gun was probably not made in Belgium; I think it is French. Belgium, especially the Liege area, was a major gun making center. In the late 19th century, entrepreneurs bought up surplus military guns by the train-load and had them converted to shotguns; many were worked over in Belgium and of course had to be proved (or "proofed") there, accounting for the Belgian proof marks. Once converted, the guns were sold all over the world, the U.S. included.

Jim