The S12K is an AK-47 frame modified to fire shotgun shells in a semi-automatic fashion. It uses smaller shells than the pump-action shotguns (with fewer pellets) so a single point-blank shot is not enough to instantly kill, a second shot is required. This is offset by the S12K's higher rate of fire, which can make it very lethal in close quarters against multiple targets. It also reloads much faster than the pump-action shotguns.
The S12K is less accurate than the pump-action shotguns and due to its semi-automatic fire suffers multiple shot and a recoil penalty as well, but being a shotgun, pinpoint accuracy is not very important. Unlike the pump-action shotguns, there is some recoil benefit to zooming when using the S12K.
The s12k or Saiga-12 semi-automatic shotgun is manafactured and produced by Izhmash primarily for Russian law enforcement and security units. The design was based loosely around the AK-47 but this weapon has only one firing mode. The S12K uses smaller shell sizes than conventional pump-action shotguns and therefore it causes less damage although it is ready to fire again more quickly. As with all shotguns it will kill point blank but has bad recoil and added to that you can quickly and ineffectively use up all your ammo, it can be wise to switch to a pistol. 1)