It was at one point going to be the replacement for the M16/M4.
@txradioguy Speaking as a former 11F4S,that seems to have been an EXCELLENT idea to me!
The M-16/5.56mm rifle and round were designed for close warfare in a jungle,with rare shots more than a few feet away. Worked fine then and there,but now our troops are working in wide-open mountainous areas,and might have to shoot across a valley at a target on a hill on the other side. Which means they need a longer and heavier bullet to fight the wind and still have enough "steam" when it gets there to take the enemy out.
They really should have adopted that rifle as the Main Battle Rifle.