The barrel in the picture- Whether it is AM-23? Not previously seen. Cannon has found a bunch of scrap metal. There was a propane gas cut in half. There might be different guns? (google translate )
I don't know if that is AM-23 barrel, but the receiver surely is from AM-23. I imagined that this muzzle brake could be useful for bomber's turrents to prevent fuselage damage by muzzle blast, but I found no picture of Soviet bombers showing it.
Is it possible that the barrel is from a water-cooled assembly, and you're seeing the part that's normally covered by the water jacket (therefore not familiar looking)?