The creator of this probably started out designing a belt-fed machine gun before deviating only slightly. A water coolant jacket would probably be suitable looking at the magazine and bolt travel distance. Apparently sold to an out-of-town gang for $800 BR.
What appears to be a home-built copy of the TEC-9 / DC9 pistol seized by police in Canada. The upper receiver appears to have overly crude welding and lacks the distinct barrel lug stampings of the original while its lower receiver has a flat non-standard profile. The open position of its bolt suggests it is likely fully automatic.
“12 Gauge made from hardware store items. The shotgun is cocked by pulling the entire barrel forward several inches until it locks into place. Then a shell is loaded through the breech. When the trigger is pulled the barrel retracts back into the receiver and carries the shell to the firing pin. Pulling the barrel forward again extracts the spent shell and tipping the shotgun to the side dumps the shell on the ground.”