We're dealing with two Murat-Cizeron guns...the original posted by French Double and the one on Gunbroker posted by Greybeard.
1. On the original from French Double:
. . . . -- "EPR.Superieur" could certainly be "Epreuve superieur" and that's probably what it is. Usually with two proof marks, the advertisement will be on the barrel as "Double Epreuve."
. . . . -- I'm having a hard time understanding how the gun could be 17.0 (16 bore) on one barrel and 22.0 (8 bore?) on the other. Definitely need a photo. Any suggestions?
. . . . -- The "B.A." has nothing to do with Jean Breuil. Here is an example of a barrel stamp with "JB"...i.e. Jean Breuil. The "J.G." above it like the "B.A. on FD's gun must be the gun maker.
Earlier on - I think he had simple "J.B." with stars before the "J" and after the "B."
. . . .-- As for who retailed Murat-Cizeron guns....just about every little hardware in France and abroad who could take an order. The 1906 Gerest-Berthon which I gave to my daughter-in-law was retailed by a store in Sicily.
. . . .-- Finally note the screw on top of the key - classic Scott Spindle. There's no patent infringement on V.C. "Helical" patent here (Thanks Larry....finally got it straight).
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2. On Greybeard's gun from gunbroker...Larry's suggestion that the retailer in Compiegne might be Guinard "Arquebusier" is logical.
The problem is I cannot find an arquebusier in France named Guinard. Marie Arthur Guinard, of rue de la Opera, Paris, mentioned above, was a retailer who stocked mostly English guns and called himself an Armurier. Here's a gushing article about the firm...
Jules Guinard of Compiegne, was an industrialist who made auto parts, sewing machines and bicycles. Where there are bikes and sewing machines in France, there has to be guns. He was so devoted to gun sports that he named his bicycles "Le Cerf" (The Deer). So normally I'd suspect He is the Guinard who retailed this gun. Here's a short history of his beginning:
However, there's a problem. From that article Jules Guinard opened his factor in 1902 in Compiegne. The gun is proofed for PS around or just before 1900 one would think. So perhaps the rue de la Opera, Paris Guinard opened a store of some sort in Compiegne.
-- Note also that the key has a screw on it's top...not a V.C. clone.