The Bushmaster really is accurate at nearly half a mile. Since that is 880 yards, then say 700 is nearly that and it shouldn't be too hard to hit man-sized targets at that range.
The AR-15 series rifles in my experience have been unusually accurate, in fact maybe even bette than your average bolt action. Using heavy bullets in the 7 inch twist barrels and they will group pretty well at 700 yards.