Yeah, the Vector is a early gun. I'm working on getting gold for it, I'm only short 4 "Blood Thirsty" [5 kills with the gun without dying] awards. Man, getting those last 4 has been rough.
Silencer and extended mags! You'll get those bloodthirsty medals. For me, it's when playing objective games. I normally get it with Domination or HQ.
I've actually been maxing out my SMGs, although I have the diamond. More XP to rank up faster.
I chose to do shotties and it's crazy hard. The first shotty is the easiest. Instead of headshots, you have to get one shot, one kill like the sniper. 250 of them to be exact.
For the headshots, use the laser sight and hip-fire!