It’s a 3-shot semi-automatic announced as a new development of “Izhevsk gunmakers” in 1959 (so it’s metaphorically if not technically the great-grand-daddy of MP153). It has alloy receiver with A-5-ish humpback profile and from the description it works on Browning’s long recoil principle. The prototype had replacable chokes with Cutts compensator.
What you think is tubular magazine is not – it’s just a hold for the barrel to travel over. Apparently, the two-shot mag is somehow housed in the receiver and/or the grip (sorta Cosmy-style).
I’m trying to figure out if it was an original development or, like many Russian guns, had a prototype in a Western gun. Any ideas?