Frags is what I use to take down shields. Come to think everything else as well.

Experimentation is necessary I'm afraid. You need to find out what works for your attack style and tolerance. When I tried mine it took a long time to make kills, which is why I favor Mr Skittles build. Frags come with a magazine of 3 for each gun. I volley all three in each pass. Reload and repeat if target is still in range (300-600m). You'll be scooting by pretty darn quickly. So, perhaps energy is the way for your build?

Good luck with it though!

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