Has to be post-1924. That's when "normal" was added to the French proofmarks. Would also have to be after France joined the CIP, because the 850 kilos is the required standard CIP proof pressure. Prior to that, St. Etienne guns carried a different proof pressure mark: crossed palms enclosing a crown, on the underside of each barrel forward of the flats. But I don't know when France adopted the CIP rules, although I think it was post-WWII. The visible "step", where barrels meet the monobloc, indicate that it's not one of the last Robusts, because those guns no longer had the "stepped" barrels.
Nice gun, and appears to be in unusually good condition.
