RE: 223 for deer?
I have made a couple headshots...years ago. I never will again. Had one experience that was so bad I won't even post it. As a matter of fact, I finished off a deer last year in doe season in WV that some expert marksman SARCASM) tried to "head shoot".
It's risky, and stupid. Like Friz said...you shoot off the lower jaw and the deer dies a slow death over a 2-week period. OR you hit the bridge of the nose, and get a deflection. That's good. NOT
Hell, I've seen butchers miss brains on a steer with a 22. AND THE STEER WAS 1' AWAY.