Electro Guns use a laser to make a vaccum tunnel through the air, then shoot a bolt of electricity through the tunnel. The electric charge shocks the target, in addition to normal damage.
Electro Guns are favored for use inside starships and other vehicles, as the ray grounds harmlessly in metal and cannot damage a metal vehicle. It is poor in vacuum, as there is no atmosphere to tunnel through and focus the beam - in a vacuum all electro guns suffer from Short Range.