From The TimeSplitters Wiki

Minigun
Ammo	400
Fire Rate bullets per sec/cartridge time	High Fire
Reload Time	Overheating: 2 secs
Damage (per Single Shot) Head/Body/Leg	?
Type	Automatic
Zoom	None
Primary Fire	Fire
Secondary Fire	Barrel spin
Games	TS, TS2, TSFP

The Minigun is an electrically-operated Gatling gun. It dispenses rounds from its six rotating barrels at an incredible rate, although continuous fire will result in overheating, at which point the rate of fire will drop to around that of a pistol. When used, there is a slight pause as the barrels spin up to speed before firing can actually commence, although the weapon's alternate fire mode keeps the barrels "warmed up" so you can fire immediately. The slight drawback of this secondary mode is that overheating will occur quicker.

A notable difference is that in TimeSplitters 1 the gun is much smaller than other incarnations and two can be held at the same time. In TimeSplitters 2 and TimeSplitters: Future Perfect, the Minigun is much bigger and takes up a bigger portion of the screen.