The M-16 ammo has the advantage of being light weight and easier to carry, but I'd still rather weigh myself down a little more and use .308 in combat, assuming my rifle is good.
I agree the ammo is light, but if it takes 5-6 hits to kill, then a soldier will need to carry 5-6 times more ammo than with a rifle with better stopping power.
OK, lets go back and look at the history of the M16/Stoner/Armalite. The round used is a full metal jacket, but the jacket is extremely thin. Upon impact, the jacket disintegrates and the bullet explodes. That's why entry wounds are tiny, but exit wounds are the size of a fist.
This weapon was specifically designed to circumvent the Geneva Convention prohibitting the use of dum-dum/hollow point ammunition, I believe after WW1.
The beauty of this weapon is that because the bullet loses form on impact, it has the stopping power of larger rounds. Therefore, troops could carry around much larger amounts of ammo without the added weight. Stoner was brilliant.
When your enemy is drugged out on hashish and narcotics, its gonna take a lot to put him down. Unless you hit a vital organ it could be tough. I am reminded of the movie Scarface where Pacino is shot over and over again and goes on mowing down his attacker, till someone comes up and shoots him in the head with a shotgun.