It only counts longshot medals which you've earned after completing the headshot challenges.
I found the best maps for getting AR longshot medals were Standoff and Express. Turbine and Carrier offer a lot of long-distance sightlines, but you're more likely to run into snipers or LMG gunners staring back at you on those maps.
Pretty much a longshot kill is the point where you can see your enemy from a distance. Like in nuketown if you camp it in the back and kill them as they come out from the side of house its a longshot kill. Use target finder yes i know it sounds nooby but its worth it. Good maps are Turbine, Drone, Meltdown, and Standoff.