From The TimeSplitters Wiki

The K-SMG is an SMG with a moderately high RoF, surpassing the Soviet Rifle by far but not quite as high as the Machine Gun. The magazine size is 32 with a max capacity of XXX. Like the Machine Gun, it can be dual-wielded. It also can have a grenade attached to the end of it, which it will fire off like a rocket(when in grenade attachment mode, only one K-SMG can be held).

The primary fire is very powerful, and very accurate, especially when compared to the Machine Gun. The reload time for primary fire mode is also fairly short.

The secondary firing mode(grenade attachment) is extremely powerful, and a direct hit will kill an enemy. The grenade will fire off in a straight line like a rocket, and will continue to go perfectly straight until it hits something. However, the ammo capacity is extremely low and the reload time per rocket is very long.

It only appears in TimeSplitters: Future Perfect, with its first story appearance being in 1924 during "Scotland the Brave". According to Anya the gun is not on record, and must have been custom built for Crow's army. It is required for the Castle Tank Boss near the end of the level.