I concur with
rookhawk and
VertigoBE. Judging by the "deep relief" type of engraving, the oak leaves engraving motive, and the very approximative anatomy of the engraved animal, this is most definitely a German / Austrian rifle.
While "deep relief" can be executed exquisitely on higher end rifles (e.g. Johannsen, Fanzoj, Borovnik, etc.) this engraving is rather cursory. This definitely leads to modest "guild" origin. The fact that there is no maker's name on the rifle supports this assumption.
I will go one step further. Unless my vision has degraded beyond relief, it is a hare that is engraved on the right side-plate (with a dog head in the background). I have never seen a German / Austrian double rifle, old or recent, engraved with a small game motive, it is always a big game motive, related to the caliber, e.g. Roe Buck for smaller calibers, Red Stag for larger calibers, Buffalo for African calibers, etc.
This makes me suspect heavily that this may be a shotgun action mounted with rifled barrels...