This is it, after toiling away in the Simulacrum and way too many forma I think this is as good as it gets for endgame.

Ever since Primary Frostbite came out, I knew the [Soma] could make it work. This build isn't the theoretical maximum damage output, but it feels really good.

Incarnon: [Soma] becoming an Incarnon weapon breathed new life into it's viability. It's skill tree and transformed firing mode are good, not great. Your 200 round machine gun turns into a 200 round shotgun, which has an interesting interaction with the [Soma]'s unique mod Hata-Satya.

• Fortress Salvo: Great skill that gives the [Soma] some unexpected utility when dealing with enemies behind cover or walls if you have more than 450 armor. Might require you to consider your Warframe's build, but these are the sacrifices us Soomers have to make. Swap Vile Acceleration with Shred and you can mow down enemies in the next room (or take a -Punch Through riven and still be able to hit behind cover). Ninjase has an excellent guide for the Soma listing all of the frames that have 450 Armor by default.

• Rapid Reinforcement: Obvious, every second spend reloading is eating into your DPS. Radiated Reload shortens this further. Also don't partial reload. Ever.

• Fatal Affliction: Since the CD boost from Zeroed In is too small to matter, this increases your damage by 40% per proc on the enemy. Needing to rawdog Cold damage made adding heat not an option, however Radiated Reload gives you more sources of status, making this bare minimum a free Galvanized Aptitude.

Hata Satya: This is a mod that's unique to the [Soma]. You can get it from Father on Deimos. The description of the mod is kind of vague and doesn't mention that it does cap out. Hata Satya resets on reload and transform and caps at 500% CC. You'll get inconsistent value while not in Incarnon mode, depending on range and enemy type. However, Hata Satya will [Reach] full stacks almost instantly in Incarnon form. So prioritize Incarnon uptime!

CC and CD: Critical Chance is nice, but you'll be swimming in it regardless if what you do. Your CD multiplier is more important as it's going to be the main source of your actual damage.

Exilus Mod: Vigilante Supplies gives you mutation and has a tiny chance of upgrading a crit, which can be helpful especially with higher fire rates. [Stabilizer] lets you focus on weak points more consistently at a greater range and is what I prefer.

Riven Mod: So here's the thing - you wanna hang with the big bois, dakka some punks with ammo to spare, make those [Rhino]'s feel insecure about that [Phenmor] they've been toting around? You need a good Riven.

The good news is, you have options. Once upon a time the perfect roll for the [Soma] was +CD +CC +Multishot. This is kind of true still, but Critical Damage is really the only one that is non negotiable. Fire Rate is great since it's DPS doesn't have diminishing returns at the cost of ammo. Complimentary elements are great too. So heat, electricity, or cold. Negatives are surprisingly flexible. -Zoom, is obviously the gold standard, but since the [Soma] has tiny little stats that get massively boosted from outside sources, you can get away with damage penalties that would ruin other weapons.

Tldr; Replace Critical Delay with a Riven ASAP CD>Fire Rate>CC>Multi>Cold/Elec/Heat

"Where are the faction mods?" I hear you screaming with tears in your eyes. Simple. I don't really like em. But if you must use your meticulously curated collection Prime Banes, just swap it for [Hammer Shot].

"Where are the damage mods?" I'm sure you've heard already that Damage mods give diminishing returns late game. You want damage from sources that are multiplicative rather the additive. The mods with wack math problems on them are going to perform better than the one that say do more damage.