From The TimeSplitters Wiki

The Plasma AutoRifle is a futuristic automatic rifle with a very high rate of fire. It has appeared in TimeSplitters 2 and TimeSplitters Future Perfect.

The TimeSplitters 2 version fires white plasma laser bolts primarily and has an under-mounted plasma grenade launcher as its secondary fire. You can carry a maximum of 200 laser bolts and 20 plasma grenades for it.

The TimeSplitters 3 version fires only red plasma laser bolts, dropping the grenade launcher entirely. However, it does have a zoom feature(supposedly because of the scope on top), something that the TS2 model lacks. The maximum amount of laser bolts you can carry for it is 400.

Both versions, when fired full-auto, start off with a moderately high rate of fire, with the RoF increasing exponentially as the gun heats up, until it overheats entirely. Neither version uses magazines, nor do they require any sort of reloading. Because it takes a relatively long time for the weapon to cool down after overheating, the Plasma AutoRifle is most efficient when fired in quick bursts.