Use with [Nidus] and [Teeming Virulence] to just kill everything. The slash procs are numerous and insane. If you don't feel the damage is enough, replace [Primed Tactical Pump] with [Shrapnel Shot] for a ton of extra critical damage. It's just that it may not be necessary in comparison to being able to get +130% total reload speed due to Primary Merciless. Of course, also throwing heat on for extra damage over time. Not sure how much it actually affects the TTK, replace with Electricity if you prefer the stun.

Oh, and reload speed is necessary for this weapon. At base, you empty out the gun in 11/12ths of a second, or roughly 0.92s. On the other hand, you spend 0.5s reloading. About 65% of your time is spent shooting, the other 35% spent reloading. Therefore, reload speed is necessary to decrease this downtime. Don't worry too much about fire rate, you don't really need it with this weapon. Of course, if you do decide to use fire rate, use [Repeater Clip] since you'll be reloading so much. Surprisingly, Primed Ammo Stock can be used here, to replace Primed Tactical Pump. Just use w/e you have though, or w/e feels best. Alternatively, if you really don't care about the downtime or QOL, then, again, use [Shrapnel Shot] for the +99% Critical Damage while Aiming on Kill. You'll probably always have it up.

Take off [Galvanized Acceleration], and you only need 1 forma for this build. Take off 80% of the endo by bringing the rank 10 mods to rank 8, and you can leave the [Galvanized Acceleration] on.