Theory Build

Do not buy both Close Quarters and Monster Rounds.

Fleetfoot or Kinetic Dash, not both
Fleetfoot seems to fare better for most users
Sell Mystic Burst for gun build.

Pick based on enemy comp

Buy Duration Extender if you have 3 flex slots, sell HPW/CQ/MR first for wep slots (keep basic mag for titanic mag)

Consider buying these at this point in game

Rush Glass Cannon if you're fed for early damage stacking
Using 1 flex on Kevlar/Boundless is OK, don't use more
Sell Bullet Resist Shredder last, replace Quicksilver Reload with Vamp Burst, sell Slowing Hex for Boundless Spirit.

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Arcane Surge provides so many buffs that the annotation is unreadable, so here it is: Theoretically huge on ult and providing full auto to lots of teammates but I'm not sure how viable it is.