Galvanized Chamber - mandatory multishot mod
Galvanized Aptitude - mandatory damage mod, giving +80% dmg for each unique status affecting the target. Having just three status effects from innate elements gives +240% dmg (3.4x multiplier), and on Fulmin's Semi-auto mode specifically, this is MULTIPLICATIVE to other base damage sources like Serration/Arcanes.
Serration/Amalgam Serration - extra multiplicative source of base dmg to galv aptitude allowing you to run Primary Crux in arcane slot. If you prefer running Primary Deadhead, you can swap Serration for either Primed Bane or Elementalist
Critical Delay - mandatory crit mod
Vital Sense - mandatory crit mod
Viral + Electric - viral status boosts all damage by 4.25x at 10 and strombringer boosts electric dot by 1.9x and improves electric weighting. Electric DoT deals damage instantly and with a small AOE.