Use HQ Dex pot and do your 50s ramp up with ammunition (reload->quickreload at 1s remaining, pull at 10s remaining). Also, refreshing lead shot right before all your buffs fall off is a DPS increase.

Toggling off Gauss barrel when you have nothing to cast is supposed to be a DPS increase as long as you remember to toggle on appropriately.

The real key to this fight is having your scholar and OT put out 500+ DPS. If your group is struggling on Faust, I suggest just waiting for more gear or more individual practice on target dummys.