Instead of making Gauss Barrel not add cast times, add a seperate attachment called Quickdraw Grip:

-15% damage dealt
+30% skill speed
+5% crit chance
+20% chance to trigger Split Shot and Slug Shot's additional effect.

Gauss Round morphed into Rapid Fire Round
90 potency x stacks of ammunition (450 max.)
Additional effect: Removes damage reduction caused by Quickdraw Grip (5s)

Ricochet morphed into Bullet Hell
250 potency
AoE
Additional effect: Targets hit by this take 10% more incoming damage (10s)