From The TimeSplitters Wiki

The SBP500 is one of the most powerful weapon in TimeSplitters Future Perfect. Its like a assalt rifle. Automatic weapon with a scope. It doesn't kill in a instant but does alot of damage, it also has alot of ammo. But, it doesn't last long because it is an automatic weapon. This weapon is kinda like the SBP90s in TimeSplitters 2.