Used K-volt a lot on my last suit, I found I did better with it when I used the firing-from-hip enhance mod.
Seen players doing well with the assault scope.
With the noise it makes, the trail of illuminated bullets and low damage makes it a challenge to win with
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If you run around with other people (e.g. me and The4orTy67 running around both with K-Volts) you can get other people to finish them off, it's a lot easer.
Don't get as many assists as I should though. I have no idea how the assists system works in this game.