I know a guy in Kentucky that drops deer every year with .223/5.56. One shot kills. In fact he has used only ARs to hunt with for the past 12 years. One of the first I knew that used ARs. .223 is plenty for about any game you will encounter around here. The Inuits use .223 on just about anything they encounter up in the arctic.
I know you can take deer with things down to a 22lr. (It's a bit more complicated than typical hunting, but I'm sure most people know what to do.)
I was mostly looking at it from a stand point of having less than perfect shot placement and still having enough power to make a reasonable kill.
I don't picture .223 being very forgiving for hunting, especially if you're in some brush.