HiBC, you don't need to be in combat to realize the benefit of the quick mag. change of the AR.
They are quite popular in 3 gun and multi gun events where you shoot, move to cover or another position and magazine changes are required.
You shoot, and while moving you hit the mag release with the thumb on your shooting hand while the support had grabs for another magazine. The empty mag falls from the rifle under its own weight and the left or support hand slaps another mag in the weld.
No other rifle I know of is as fast or as easy when it comes with changing magazines on the run, without looking.
I believe that is why they are so popular in competition.
It worked the same way in combat, the point man, empties his clip full auto and falls to the ground as he reloads, the slack (guy behind the point man) does the same thing when the point man drops, then normally (the way we did it) the '60 gunner is right behind the slack and is now ready to move up and take up his position while the rest of the squad forms a line.
Again, I've never seen a rifle that worked better in these cases.
I've done most of my match shooting with a M14 or M1A, you have to take your shooting hand off the pistol grip to change magazines. In high power that's not a big problem.
The way I did it was to fire my first two rounds, roll to the left a tad and change mags while I'm looking through the spotting scope at my first two hits to see if I need a sight change. But in this case I'm not running to cover or to a new firing point. Plus I have 60 seconds to get in position, shoot two, look load and shoot 8 more. Thats a lot of time, in 3 gun or multi gun you don't get the luxury of that much time.
As too the AR forcing your head higher, putting you in danger.......all I can say its a none issue.............probably the dumbest thing I ever heard about ARs.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071