The Lightning Gun has perfect accuracy, meaning if you miss, it's your fault. Hitting airborne enemies from below with a continuous stream will pin them in the air.
This is the gun you want when your fighting mid-range and also when you have the quad. One of the guns you should always try to get. To aim properly, keep the mouse still as much as possible (corrections are recommended) and travel in the same direction your opponent is moving. for example, if your enemy is running to the left, do the same to keep the beam on them.