Dig - I really hate to tell you this, but...
The design philosophy behind the .223 round WAS to create a lightweight round that would increase the carryable amount of ammunition in the basic loadout, and with increased potential for grievious wounding rather than actual killing power. (fmr) Agent Vince is correct in the assessment that the .223 would wound rather than kill, and the lightweight bullet would likely tumble within the body increasing wounding and decreasing the possibility of creating "walking wounded" - tying up a minimum of three enemy soldiers for each one wounded (two to carry the man, one for his kit.)
This does NOT discount the fact that the .223 can kill - it has been used to great effect for exactly that. Any bullet, with enough power and properly placed, will kill. In the 'high volume' tactica used on the common battlefield, the intent is to tie up as many files as possible when shooting - and causing THREE rifles to be taken out of battle for just ONE wound is not a bad thing - militarily speaking.
The .223 was developed as the .222 (IIRC) was evaluated for use and found lacking. Reference "The Complete AR-15/M-16 Sourcebook" by Duncan Long, available from Paladin Press and better bookstores.
FFZ