Finally got it after wasting my time with core (domination, Hardpoint, Nuketown etc.)
Couldn't get it in hardcore kill confirmed, but after a fruitless 90 minutes of going 7 kills then getting killed in Domination etc, I decided to give Hardcore another chance with only ten minutes before I had to leave for class. Picked up someone's M27 with target finder and a silenced MP7 and got it on Raid hardcore kill confirmed.
The enemy had a UAV, and I nearly had a heart attack. I camped in the garage for two kills then went into the room in front of the garage. Got a few there. But then a teammate put up a guardian right next to me. So I decided to camp looking at the windows, and sure enough a straggler tried to come in to destroy the guardian and I got him for the tenth kill.