I just started going for diamond assault rifles. I already had the 100 headshots for the MTAR, Type 25, M27 and SCAR-H so I got those out of the way today. I'll probably knock out the FAL OSW tomorrow and try to make some headway on the SWAT-556.
I actually enjoyed going for those gold camos. It took me about six or seven games with each assault rifle to get them gold. My KD actually went up, which surprised me. I had two EMP grenades and two concussion grenades to help me out. I didn't run a secondary because I like the longer sprint duration with the combat knife.