There are several possibilities for the mechanic B in the trade as some point post 1900 there was an Emil Bader-Mehlis, Edmund Bader - Suhl, Engelhardt Barthelmes - Zella Sankt Blasii, Emil Barthelmes - Zella, Ernst Barthelmes - Zella, Edmund R. Bornmüller - Suhl, Ernst H. Bornmüller - Suhl, Ernst Büttner who may have gone by Ernst Wilhelm Büttner and I for one think the mechanics used the last to letters for initials. I'm sure there were others like Ernst Bauer who may have had a repair facilities or have been a stocker. At 1st one would think Suhl makers would have sourced Suhl makers but it is possible that effort was sourced from Mehlis & Zella Sankt Blasii. With that said a 1st guess would be Emil Barthelmes who hung out his gunmaking shingle in 1854 so there could have been a couple of generations by the time Max Metzner owned the firm post WWI.

Kind Regards,

Raimey
rse