That shotgun has obviously seen some rather extensive use. It is an old underlever shotgun, possibly 1880 to 1890s. Underlever shotguns never fared well in the US, we use mostly top lever guns, but there were some made in the the US during that period.
If this shotgun was made in Europe (which is likely for an underlever), there should be a series of proofmarks on the bottoms of the chambers; the smaller secondary underlever should spin in the opposite direction to let you take the barrels off, and if you can take some pictures of any of those marks, you'll probably get some more information.
I have a couple of old catalog reprints, you might be interested to know that a shotgun like that cost $7.00 in 1901. Conventional toplever hammer guns were $7.45 for a cheap import on up, with the Sears house brand starting at $10.95 and a Remington for $21.00.