Jump and dump. That's what I have done to get the 85 or so that I have and I haven't even been trying to get those. Jump, spray the entire mag from the hip in the general direction and typical it results in a headshot.
Executioner headshots are easy this way as well.
"Cover your receptors Perceptor." Driver picks the music. Shotgun shuts his cakehole.
Stun someone (twice depending on distance), run right up to their side (they will normally lie down making it easier), shoot in head and grab scavenger pack, repeat x100
This works really well on FFA but it isn't that fun more of a grinding session. I was pulling in 15-20 headshots a game when I was finishing the last few pistols and SMGs. if too many people have Tac Mask switch lobby.