Assuming the CMR under "Choke rectifié" has something to do with the maker, according to https://www.passionlachasse.com/t28729-identification-fusil-darne-cal-12#817725
Quote:
the "CMR" stamp is that of the barrel-making company of Champaley, Meiller et Riou, very famous in the Saint-Etienne basin at the end of the 20s and 30s, your rifle is very probably from this time of manufacture.


More Frenchies with CMR on the barrels:
https://www.shotgunworld.com/bbs/viewtopic.php?f=5&t=469074

https://www.passionlachasse.com/t35447-fusil-de-chasse-francisque-darne

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