That was my thinking Rondo. That carving gave it away. I think a bunch of those guns were made in Belgium and imported weren't they?
I think most of them were Belgian made,... maybe a few also from Spain.
Under the barrel (in the area covered by the stock) might be a number, indicating the metric size of the smooth bore in millimeters.
And yes,.... there were quite a few of the percussion guns imported to South America in the early 1900's, for bird and monkey hunting.