I seem to have a hate/hate relationship with most or all of the NC weapons. I've gravitated to using the Warden with a 3.4x chevron-scope on my main Engineer role as it's fairly accurate out to long-range and can headshot people. I've just added a foregrip to it to reduce the recoil so I can attempt to double-tap people but I've yet to try it out.
The Sweeper shotgun is my other weapon of choice to most other classes. After unlocking slugs for it I can drop people in 2-3 hits and the x2 or x3 red-dot sight works well outdoors for short-sniping but the dropoff on the slugs is horrendous which puts a damper on it at far-medium range and beyond. Which is about right, I think.
The Jackhammer is absolute toilet. THAT I am gutted I spent money on and it can't even have slugs like the Sweeper can. Don't bother.