If you re not a fan of changing Primed Bane Mods from time to time then replace Primed Bane Mod with [Serration].
Viral always go good with slash, hence Hunter Munitions is added.
Point Strike > Critical Delay, with Primary Merciless Maximum Ammo would reach 40/800 and we want to max out the potential of the weapon so decreasing it's fire rate would hurt the weapon a lot.

Ammo pickups/efficiency of this weapon is really good even without [Vigilante Supplies] but what we are after is the passive bonus [Vigilante Supplies] give.

If you are planning on buying a Riven the recommended stats would be:
Positives: Critical Chance, Critical Damage, Multishot
Negative: Zoom

and Replace the slot of Galvanized Aptitude.
The Forma Placements here are strategic. The last slot would be left unforma-ed until you decided to get a Riven.
I recommend not to forma the last slot up until you decided to get a Riven, so you won't waste 1 Forma if the polarity would be different.