I'm also an engineer and I use the rifle more for utility than actual damage. The grenade or bombkit out performs it for damage and gives you many more conditions to work with.

I'm personally using the grenade kit with the radiation field asura skill and stacking condition damage. Works great and I can pretty much ignore my aggro since the aoe of nades is ridiculous.

You can also throw grenades behind you as you run which is crazy.

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