Here is a build I use for hunting those Eidolon bad boys.
I use a riven mod in replacement for the heavy caliber, you can do that as well if you want to. You will want anything that increases status damage (Radiation), damage, or multishot.
brett99 suggested I add Critical Delay so I decided to swap out Point Strike with it which adds a bit more critical chance making it a bit better in the long run. Some other people keep suggesting I swap out High Voltage, I have High Voltage in this build specifically for Electricity and not the Status Chance but if you really want to you can definitely add one more Forma to replace it with Stormbringer but the purpose for this build is to be more of a budget build for people as to not wanting to use so much Forma on a single weapon or a weapon you would use for a single purpose.