My first build, but from my testing it melts level 100 Heavy Gunners.

Sure Shot - Adds additional status chance to help boost the weapon over 100%.
Hornet Strike - Mandatory mod, increases overall damage.
Barrel Diffusion - Mandatory mod, more projectiles.
Slip Magazine - I found the magazine capacity of the weapon to be too small for my liking (making it feel restrictive). Adding extra capacity grants freedom to hit more enemies and proc status effects.
Pistol Pestilence - Adds toxin damage, boosts status chance.
Jolt - Adds electricity damage, boosts status chance.
Scorch - Adds heat damage, boosts status chance.
Lethal Torrent - Additional fire rate, increases multishot.

The new galvanized mods seem they would help further this build, but I haven't got my hands on them for now. Feel free to swap them in however and see how they perform. This build does help serve those without the new galvanized mods at least.