Rubico Prime Build

[Nudelhut]

I wanted to ask how I can improve this build further. I want to use it for Eidolon Hunts. (I don´t really have platinium for a riven.)

https://steamcommunity.com/sharedfiles/filedetails/?id=1629959319

[Watermelons]

Swap out Corrosive for Radiation damage. Corrosive has no bonuses on any of an Eidolon's defenses. Their health takes +25% extra damage from Radiation and their armor takes +75% extra from Radiation.
Now, if you're running a premade group, or coincidentally a group of public players, who all run with Corrosive Projection, then Electricity would be better since it gains +50% extra damage to Eidolon health. The armor resistances/weaknesses wouldn't be considered anymore, so you'd only care about what damages the health most.

Besides that, nothing much else can be improved, except maybe getting rid of Hammershot ( its bonus isn't particularly great, and Status is useless against Eidolons excluding from Amps for a particular set up ). I could suggest Vigilante Armaments. It costs the same mod space, and gives you another 60% multishot. That takes your current 90% and makes it 150%, which means you now have a guaranteed double shot ( therefore, guaranteed double the damage ) plus a 50% for a third shot.

[Nudelhut]

Thank you, I didn´t know radiation damage was better I will change that. Vigilant armaments is already installed its "Vigilianten Aufrüstung" I just put hammershot in there because I didn´t know what else to put there

[Watermelons]

Oh shoot, I don't know how I mistook that for something else, I can even recognize the picture and know enough German to guess its meaning.

Well then Hammer Shot is alright, unless you want to swap it out for a 60%/60% elemental status mod like Thermite Rounds or High Voltage for a bit more damage, unsure if the math will be in its favor or Hammer Shot's.

Another possibility is Argon Scope if you have it. You may not be able to damage an Eidolon directly until you destroy all of its limb sections, but you can still shoot its head once to gain the Argon Scope buff, then hit the limbs. And then in the final section, it just further helps you kill it faster by giving you that extra crit chance on top of Rubico's scoped crit damage multiplier.

[Huillam]

If you have the formas for:
http://warframe-builder.com/Primary_Weapons/Builder/Rubico_Prime/t_30_22332240_132-4-5-137-1-10-138-3-5-140-7-5-141-2-5-150-0-10-159-5-5-784-6-10_150-8-137-7-141-6-138-6-132-8-159-5-784-8-140-9/en/2-0-123/197060/0

If you don't that one should fit your current polarities:
http://warframe-builder.com/Primary_Weapons/Builder/Rubico_Prime/t_30_22032200_132-0-5-137-4-10-140-5-5-141-3-5-150-1-10-159-6-5-329-2-3-847-7-5_132-8-150-8-329-7-141-6-137-7-140-5-159-9-847-9_WyIxIiwiMCIsWyIiLCIiLCIiLCIiLCIiLCIiLCIiLCIiXV0=/en/2-0-123/
Swap Vigilante Armaments for Argon Scope if you have it.