In my opinion, the "16BN43" would be a marking of the Brits, prior to the gun have been transferred to the post WW2 Austrian Police, as it is similar to other markings occasionally seen on BSRs, as applied by unit armorers during the guns service with the Brits. "16BN" would have been the unit and "43" would be the unit inventory, or rack, number. An inquery to the Imperial War Museum in London will probably get a reply that identifies the 16BN . Ed