Why is it????? Why does everyone love 11.5" barreled ARs WITH A 5.5" flash hider attached? I understand loving them when they are SBRs with a birdcage or a 4" sound/flash moderator. Quite sexy and they make an effective close up SMG. BUT with a permanently attached flash hider to make it 16", you are robbing yourself or performance. 11.5 inch ARs do maybe 2700 fps with M193 and 2600 fps with M855 ball. Problem is that fragmentation is not assured until 2700 fps, and rarely at 2600 fps. My M1carbine with SP ammo duplicates that kind of performance easily. MY XM clone with a 16" pencil barrel and the birdcage is only 1.25 inches longer and gives about 3100 to 3150 FPS. That is reliable fragmentation from 175 to 200 yards. If you have to have the XM177 look, use a slip over like I did and get that extra 400-450 fps! Enquiring minds just want to know. I see tons of them for sale on GB. Mine is a house/farm gun. I know it will work out to 200. Yes, if you use EXPENSIVE 75 grain TAP it may work, but mine works great with M193!