Can you post the spec your running with? Also what skill priority do you use?
This is the spec that I generally run for PvP http://www.torhead.com/skill-calc#801RRGbdRrogzZMsoZb.1
You can of course swap out a few things based on personal preference. My skill rotation is generally Sticky Grenade, Storm, Stock Strike, HIB, Energy Blast. Then I use a priority of HIB > Stock Strike > EB> Everything Else.
Use both taunts on cooldown if possible. And always have guard on someone preferable people who are being focused.
Also, what rifle are you using? I kinda like the blocky, round barrel of it.
Champion's Supercommando' Rifle