I'd also like to know when that "in house" proof-mark began, when it ended and who had the right to do this.
Here is another AB....key and entire gun not pictured but there is an AB surmounted by a crown on the barrel flats, AB on the barrels and it has four crossed fronds or palms on the flats in addition to two Saint-Etienne proof marks and Jean Breuil barrels....interesting.
https://www.shotgunworld.com/threads/any-idea-of-this-french-shotgun-id.497178/![[Linked Image from i.imgur.com]](https://i.imgur.com/1qKZYTu.png)
I've searched "Armurerie Bxxx" and "Arquebusier Bxxxx"...all sorts of names - tried to find lists of 1920's Stephanois gun makers, etc. No dice so far.