What options do you have at your range?
Usually I like to start with ready-ups. Gun low, bring it up, turn safety off, BOOM 100yd head shot, safety on, down. 10 times.
Then I like to set up a course. 25 yard run, drop to prone, 3 100yd headshots, 25 yards forward, drop to kneeling, 5 COM hits, 25 yd run forward, drop to squat or shoot offhanded from cover or something, 5 COM hits, approach target and shoot 10 more rounds while walking COM at any range your comfortable as long as you keep moving, safety on, transition to pistol and 5 to the head, 5 COM in any fashion you like.
Safety has to be on while moving, throw in at least one mag change or two, when you get bored have your competitor load your mags for you and sneak two snap caps or dummy rounds in. I love the added surprize of failure drills when you have no idea when its coming.
Time it. 5 seconds added for each miss. It's not as easy as it looks if you play fair. (As keeping your form neat, not just flailing about out there.)
My moneys on the AR10, especially if he has a good Aimpoint, Eotech, or Acog.