do you use 1st or 3rd person? ...its much easier in 1st person. If you want lotsa headshots, use the storm trooper, 1st person and use the scope for most of your kills (it doesn't zoom very far so you can pan fast, and the auto aim doesn't interfere as much). The trooper's rifle is deadly accurate for the first 4-5 shots over a moderate distance and because of its rapid fire you can get up to 3 head shots per kill if your shots are on point.
I just run around with the trooper in first person then use the scope every chance that I can. My best was 67 headshots on bespin platforms with 121 kills doing this.