The NATO 5.56 was designed to not tear people up... It's main purpose is to penetrate and come out the other side intact, but there is a lot more involved than just the bullet... (After reading wikipedia
I seem to be wrong on this, but that's what i've always been told) One of the major things that determines how bad a bullet f's you up is rifling twist rates. Luckily the US military has spent a small fortune finding out what rifling twist rates do the least damage. An example of this twist rate application is the M-16 used in Viet Nam by the US back in the late 1960's. When the war started out in 1965 or so, (The M16 was first adopted in 1964 by the United States Air Force) the M-16 started out with 1 in 14, or 1 in 12 twist, depending on which report you read from different branches in the military. There were all kinds of reports about the bullet "tumbling", and as a result the 5.56mm round was really tearing people up. The reason for this is because the bullet wasn't stabilized. When the army found the heavier bullet, 63 gr., penetrated body armor better at long range, the twist rate became 1 in 7 as it is found today and the tumbling stopped. When you order a new AR-15 or M-4 or whatever you can pick what twist rate you want the barrel to be. You can get 1x10 twist, 1x6 twist, 1x7 twist and so on depending on what type of bullet you are using and what type of target you are aiming at. I know all this because the last AR-15 I built I picked each part out myself so it's totally a one off.
As for the comment on the bullet not being very powerful -- that's personal taste I guess... I've seen reports of 3100 Fps with an 80 grain and 2700 FPS with a 120 grain. I've also heard 20 Tactical - 33 grain Hornady was reported to hit 42-4300 FPS in a 24" AR 15... This is pretty impressive.
Here is what the pros say about 5.56MM & 7.62 rounds: http://www.globalsecurity.org/military/ ... 86/MVT.htm
The 5.56mm will, at best, only be an interim NATO standard. Due to its small size, further improvements of the 5.56mm will be insufficient to keep up with the changing requirements of future battlefields. Overall, the older 7.62mm NATO is a better standard cartridge since it has the capacity and the flexibility to be significantly improved and thereby remain effective.
guess it's a good thing to have both...