what I have learned ofver the years was that the common hunter only get a shotgun for years but he had to join a local hunting club. surprisingly shotgun cartridge handloading was common over the decades but before WW 2 only with blackpowder, after the war blackpowder and smokless powder. I have see such a smokless powder can with reloading data for 12 and 16 ga. the powder was the same the russians load in 7,62x54R blanks, NO DOUBT.
I have some russian brass shotgun cases in 12, 16 and 20 ga.( they made 24, 28 and 32 brass cases too) and some of them have the typical traces of blackpowder loads fired.
something that puzzle me is the 8,2x66 SR hunting cartridge from the 1930s with its low velocity and lead bullet. I would not wonder if this round was loaded by hand with blackpowder.

btw, the russians were not different from other people and hide all kinds of illegals guns