I'm requesting that good 'ol laser cannon from Half-Life. You know the one, it shoots a short green laser on primary fire, yet charges up and creates a large explosion with secondary fire. Its icon is also the base for the modern physgun's.
Name: Tau / Gauss Cannon
Range: Medium to Long
Primary attack: Fully-automatic, 20 pts/beam
Secondary attack: Charged-up shot, between 10 and 130 pts/beam
Ammunition: Depleted uranium
Capacity: Ammo reserve of 100 units
It doesn't have to do the amount of damage it's supposed to do, in case you think it might be too powerful.