Florence Nightingale Award Achievement

[360GamerJ]

I can't get this achievement to unlock. I shoot my teammates until they are incapacitated and then use the field dressing to heal them. I have done this more than 20 times already but it still hasn't unlocked. Has anyone else had this problem?

EDIT: Turns out that it hadn't saved any previous attempts when I checked the stats and I only had 1 teammate healed at the time of posting this topic. I just unlocked it.