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.