This gun was probably produced during WWII by Remington. While the Nazi's took over the Belgium plant, Remington produced the Auto-5 under the Browning patent. The B stands for 12ga (A=16Ga, C=20Ga) and the 31398 is the serial #. As far as I can tell, Remington built these guns from 1940 until 1946 when production went back to Belgium