How about a coilgun? Basically the same thing as a rail gun but fires smaller projectiles and has a larger magazine. It could work like the fusion rifle to where it has to charge before fired, but unlike a rail gun wouldn't have to be reloaded after every shot. It could also have maybe three or four shots to use before being reloaded and would deal a small amount of splash damage. Also being a one-shot-kill to the torso or the head.