They told us in the military that the object was to create as many causalities as possible. Basically if you kill one guy you have one guy out of the fight, if you wound one it takes more people to evacuate them, taking more people out of the fight. And they added commanders, that don't take care of their wounded quickly lose the confidence of their soldiers.
That is the talking point anyway. Whether it is fact or fiction I have no idea, above my pay grade.
I always did wonder about it also causing manpower drains on the us, caring for enemy casualties. Those talking points always did strike me as salesmanship.
One talking point did make sense, .223 rounds are lighter and you can carry more ammo. Soldiers in combat are notoriously bad shots, quantity versus quality.
I always carried the "Pig" M-60 machine gun, I was loath to be under gunned. Sure I sweated more, but I had a lot more confidence.
The M-2 was even better.