• [Hunter Munitions] for slash. Everyone seems to forget it's only a 30% chance to inflict a slash proc. Generally multishot, high fire rate or orange crits makes up for this, but here we have none of those without getting a few kills first.
• Vital Sense so that your crits do more than change the text colour.
• [Point Strike] for a usable crit chance at zero stacks, and a chance of orange crits at high stacks. Without this you only get 55% after headshot (compared to 90%) , and only barely reach 100.8% at max stacks.
• Galvanised Scope to actually be able to reach 100% crit chance. As such, headshots are a must.
• Galvanised Chamber for multishot. The most important stat on any build, as now that 30% chance for slash is looking more like 90%, and that 90% chance for viral is now all but guaranteed, and both now with chances of multiple procs.
• Malignant Force/[Rime Rounds] because we can't have viral without viral mods. The status weighting could be better, but we start running the risk of not getting viral at all, as well as needing another forma. At least magnetic is basically viral for shields.
• [Hammer Shot] is the flex slot (unless you [Hate] consistency and want to swap out [Point Strike]), but honestly I would not recommend swapping it out. The increased status chance bumps viral from a 66% chance to a 90%, making you not as reliant on multishot just to get a single proc, and the extra crit damage helps it hit that much harder.
• Given we're going for headshot kills anyway, Primary Deadhead is an easy choice. The extra headshot multiplier helps as well.

Possible alternative mods are:

• (Primed) Cryo Rounds for more upfront damage and better status weighting. Extra forma needed.
• [Bladed Rounds] for more damage. Best swapped for Point Strike alongside Primed Cryo Rounds as in terms of raw damage, it beats out Primed Cryo Rounds by only 1%.
• Bane mods would probably have enough dps to make up for the lack of viral without the increased status chance.
• Primary Merciless still isn't exactly bad, it's just deadhead is better and you need to make the effort to make this build work anyway.

Given how this build already needs to spend an extra 2 mod slots on consistency rather than damage, you're probably better off sticking to external fire rate buffs.