The city of St. Etienne was an important early gun making center in Europe. Tradition holds that the king of France, Francis I, helped jump start the gun making activity there in 1535. Before that, like Liege and other cities, it had a tradition of making arms and armour. The history of the Proof House in St. Etienne is a bit serpentine. The gunmakers had been doing their own proofing. Louis XIV appointed a noble to oversee the quality of firearms (armes à feu, literally Arms of Fire)by 1665. Eventually, through government regulation, the Proof House grew.
Like Liege, Birmingham and other locations through out Europe, a community of gunmakers lived and worked there. Their work was sold through Europe, the Mediterranean and well into the Ottoman Empire.
Post some pictures, would like to see them. Some one may be able to recognize a maker's mark.
Pete