The guys down on Harley's Forum can tell you more, but Dimoulin was a known name. If not forged, and with steel barrels vs twist or Damascus, it's probably a shooter with a bit of collector value in good condition. It may be Belgian, a stamped ELG will show so.
However, all old guns should be checke dout by a competent gunsmith before use. This is almost certainly a shotguns with 2 1/2" chambers, some can be converted safely for standard modern ammo, but not all. Shooting modern ammo in an old short chambered shotgun is neither fun nor safe. Some low pressure 2 1/2" stiff imported, not cheap, and making new short ammo isn't that difficult for a reloader.
The good news is that all of these old hammer guns I've handled and shot were sweet indeed. High marks for handling,balance and effectiveness on upland birds. Enjoy....