Hey, I've parsed as Machinist with the ACT update today, and the results seem to be quite disappointing with Gauss Barrel toggled.

Having Gauss Barrel toggled the whole time even with optimal positioning (staying in 1 spot) does the least amount of DPS, meaning that for the majority of the time, you should have Gauss Barrel toggled off.
However, having Gauss Barrel active while you have your buffs like Hawk's Eye/Blood for Blood/Dexterity Potion/Raging Strikes coupled with Wildfire is a lot stronger than not having Gauss Barrel active. The best time to cast Gauss Barrel seems to be before Hawk's Eye when you gain a Slug Shot/Clean Shot proc so you don't have any cast time on the shots when Gauss Barrel is active.

Can anyone else confirm that having Gauss Barrel on for the opener and hard casting Gauss Barrel when buffs are up otherwise having it disabled is the highest DPS?