I found these two post in another forum.
"The Hamilton Arms shotgun is a trade name of the Wiebusch and Hilger Co of New York. The Hamilton falls into the catgory of a "Hardware Gun" in that it was probably made by another company for Wiebusch and Hilger. Many of these shotguns were made or imported by Crescent Arms. Although the Hamilton is not specifically mentioned in the Crescent Cross Over, the shotgun could have been made by a company in Europe, (Belgium,) especially for Hamilton, a situation similar to the Crescent Company."
"According to Side by Sides of the World by Charles E. Carder; Hamilton, W.H.: Belgium proof marks, circa 1870-1880, lower quality, history unknown, 12ga, sidelock, outside hammers, Damascus barrels, pistolgrip, splinter forearm, rib extension, steel buttplate, top lever opener."
Hope this helps. If it is Belguim you can tell from the proof marks on the watertable.