Re: 5.56mm and "wounding".
The basic concept behind the 5.56mm round initially becoming US/NATO standard is very simple. You can carry more of it. The wounding thing was a nice social theory tacked on back.
All of the studies from WWII and Korea showed that the single most limiting factor in infantry firefights was ammunition. At ranges beyond 100m or so, the ability to actually hit anything drops dramatically when you factor in a combat environment.
So, the NATO guys decided there's three ways to solve that:
1) Fire lots. Lets say it takes on average 3000 rounds per wound/kill. (it got as high as 10,000 in vietnam). If a soldier can carry 300 rounds of 5.56, and only 180 of 7.62mm...you can get more hits per load.
2) Get in close or a good position. This requires moving. And moving equals dead unless the enemy isn't shooting back. So you spend prodigious amounts of ammunition keeping their heads down. The more ammo you have, the longer you can cover movement.
3) Hope the other guy runs out. if you pop and shoot one round every 5 seconds, and he pops and shoots one round every 5 seconds, and no one is really hitting anything...you win by default when he runs out a hundred rounds before you. Or he starts conserving, and now you can move or take well aimed shots since very little in the way of bullets is zipping back your way.
Add in the fact that people figured on having to fight a 4:1 odds or worse against the USSR, and you simply couldn't "hold the line" with the ammo you had for larger rounds. You have to remember, this concept was designed shortly after experiencing massed infantry attacks in Korea, and when it was expected the main role of the rifleman was to hold or take the last 200-300 meters while tanks and support weapons produced the mass casualties.