This is an old (relatively; production began in 1964 and I'm not sure when they stopped making them) Tula TOZ-63 double barrel shotgun. These were made in 16 and 20 gauge. This one is a 16. I have never seen a 20 gauge version.
These Tula shotguns have nothing to do with the common Baikal double barrel shotguns that are produced by Izhevsk. The Tula is a true side-lock gun with a Greener type crossbolt rather than the cheaper-to-produce boxlock of the Baikal, and it is of substantially higher quality than the Baikal. Not that the Baikal is not a functional shotgun, but if you see one of these Tulas for sale, I recommend grabbing it, as it makes a wonderful homestead gun for hunting, varmint control, and even defense.
Possum living is all about living on our own terms, slowing down and kicking back and doing what we really want to be doing instead of burning ourselves out in the pursuit of what society tells us we should strive for. It is about finding easier and more interesting ways of providing what we really need, as an alternative to paying the high price in time, money and freedom that society extracts in exchange for servicing these needs; and about finding the strength to say no to those services we don't really need.