Timesplitters Future Perfect - Gun continues to move

To make this trick work you need a machine gun style weapon, such as:
Machine gun
Mini gun
Soviet Rifle
K-smg
etc.

Fire the gun for a few second and hold in the Z button (or throw a grenade if you aren't playing on the gamecube) continue to hold Z after you stop firing the gun, and then watch, the gun will continue to move as if you were shooting for several seconds.