Probably not a question that would generally be asked here at ALR as shotguns are a very different breed of firearm. This being said...
I expect your shotgun will bear proof marks hidden by the stock on the underside of the tubes. Most likely Belgian proofs, but Birmingham is possible. Generally the Birmingham guns are a bit better than their Belgian counterparts but there is no difference in value to speak of.
This is a utility piece in all respects. It was made for the trade and is not highly prized by collectors unless in as-new condition, however there is (Maybe "was" is a better term considering economic conditions.) a market for these old pieces as display decorations.
The muzzle loading shotgun in more or less modern configuration arrived here in the US just prior to the Civil War. It existed in Europe a few years prior but it's safe to merely say c. 1860. A decade later these pieces were rapidly being displaced by breach loaders and by 1880 they were almost forgotten.
My guess based on what little you were able to share is that you have a rather late Belgian muzzle stuffer. Had the piece been manufactured a year or two later it would have been a breach loader.
You have an interesting bit of history in this shotgun. Whether it never did anything but protect the local chicken house or whether it provided much needed protein for a rural family, the gun served a purpose. Value will be found in family history and the connection it has with this old grocery-getter. Enjoy the piece and value it for what it is.
