Yessir, it IS Belgian - the third image clearly shows the 'Perron' - the monument trademark of any Liege-made gun.
As for bits and pieces, well, you've had it. These guns were made in the hundred thousands for the likes of Sears, Roebuck and others like them, and sold for around $10-25 or so at the turn of the last century.
The stamp nearest the ejector in image 5 is the 1893 black-powder proof stamp in accordance with the German proof laws of 1891.
18.4 is the bore diameter in millimteres, indicating a rather 'open' 12 gauge tube.
The curly intertwined letters EL indicate proof after 1894, and are the mark of an allegedly superior quality provisionally-proofed barrel. ELG is the Liege proof-house.
tac