the only thing that matters is that none of the bullets miss a target.
i have dictator and whatever the sniper one is. here's a few tips for getting this:
-go into a cage match and just tell the person your going for this (9 times out of 10 the person will want to do headshots or something so you can easily trade challenges here), or just boost.
-lightly tap the trigger so that only one bullet fires at once, b/c often times you'll hold down the trigger and a few bullets will fly past the body after they've died.
-aim for their legs so that they take the minimum amount of damage and you can fire more rounds without them dying
-use a silencer and make sure you do NOT have stopping power or FMJ on, for the same reasons as the last point
-use whatever gun has the shortest clip/least power
-fire from a far distance to decrease damage, but don't fire so far away that you miss your target.