Lambert & Bruyninck or possibly Lhermitte and Bruyninckx (but usually LB not L&B)
http://littlegun.be/arme%20belge/artisans%20identifies%20l/a%20lhermitte%20and%20bruyninckx%20gb.htm

Proved 1910-1921 (no lettre annale)
Barrel weight at the time of proof 1.333 Kg = 2.94#. If > 3% less now considered out of proof.
Original bore 18.3 mm = .720mm
L choke 17.3 mm = .681" = .039" = Full
R 17.6 (or 17.8?) = .693" = .027" = Imp. Mod.
70 mm chambers