Double epreuve means double proof, which is confirmed by the proofmark, repeated twice, you see on each barrel in front of the flats. The 65 means 2 1/2" chambers. Montargis is a small town (about 20,000) in France. Poichauvin is probably the name of the gunshop owner in Montargis who sold the gun. That Roncharc-whatever was probably the barrelmaker, maybe the maker of the entire gun. But what you have, essentially, is a fairly standard St. Etienne boxlock. Pretty much the French equivalent of a Birmingham boxlock. And, in this case, like a lot of Birmingham boxlocks, you've got the name and location of the shop where the gun was sold rather than more specific information about who made it (other than the Roncharc stuff). Very much standard French proofmarks, although the double proof indicates a pretty stout gun. All the references to choke don't tell you anything about how much choke there is. (French guns never do.) They're likely pretty tight.
