Alexey, I believe it was liberated gun from Germany and there is nothing to do with Russian customs in this case.
I wonder if there is a reliable way to tell if the gun was "liberated" or if it remained from earlier times? The owner's words are not to be trusted entirely. You know how many postwar guns were sold as "a Goering's gun". I think it's not always a fraud, just stereotypical thiinking: "if it's old and German, then it was a war trophy". Sometimes, this comes from original owners - I've been talking with my Grandfather a lot lately, and he recalls that after the war and all the way through the 1960's people were afraid to admit they had money (if they did). So, if they got a "luxury", like an expensive shotgun, and someone asked where it came from, they often lied. "I got it as a bonus", "I won it at the lottery", "I brought it back from Germany"...
