There is a post on Passionlachasse that suggests the AB might be Breuil-Aulagnier. Here is why I think this is doubtful. Here is a collage of 8 Breuil-Aulagnier barrels. On none of these guns is there a BA or AB on the Key. There are stamps on the barrels for "Breuil-Aulagnier"..."C.Breuil"...."BA"....."CA." There is one stamp "BA" with a crown over it in an oval which might be related to our AB above but doubtful.

[Linked Image from i.imgur.com]

Baluch are not Brahui, Brahui are Baluch