Here in New Zealand the .223 has killed literally tens of thousands of Red deer, but predominantly in the hands of professional shooters using AR15's or Mini 14's from helicopters and short range, ie. less than 100 metres and usually less than 50 metres. Head or neck shots are the norm. Quite a few are shot by hunters with this cailbre but at short range with head or neck shots. Having said that, .223 is not considered to be an adequate deer cartridge in NZ. .243 is reasonably popular but is still considered to be an unreliable killer by the majority. 7/08, 6.5x55, .308 are the most popular calibres closely followed by .270, .25/06, .30/06, then a few of the magnums. There was a period in the late'50's and early '60's where the professional ground shooters (cullers) achieved high numbers with the .222 Remington, but once again, range and shot placement was critical. I use the .223 AR15 for goats mainly but will not hesitate to take a deer with it under the right circumstances. I normally use .308 Remington Model 7 for bush work and a .30/06 Husqvarna for open country.