From The TimeSplitters Wiki

The Monkey gun is the most powerful automatic in Timesplitters Future Perfect. It is unlocked when electro chimp challenge is beaten with a bronze 'trophy' or higher. The monkey gun fires a clip of 64 bullets very quickly, and if only a few of those bullets hit, it will most likely kill the target. It is not instant kill, since one or two bullets can hit without death, but just one gits rid of almost half the target's life. the monkey gun bears and odd resemblance to the magcharger, and both are reloaded in a similar fashion. A monkey gun must be reloaded after use every time, and runs out of ammo very quickly.