I have got some questions as to the difference between the two of these calibers. I know one difference is a few thousands of an inch in headspace, but I am wondering what is the difference is in ballistic performance. I understand that the 5.56Nato is the military round, and have been told that it is a higher pressure round, and that most surplus ammo is no good for reloading. I know that varmint hunters seem to prefer the .223 because it is more accurate (so I have been told) and it appears to be more small game hunting ammo available in that caliber. So besides these differences, is there any velocity difference, and any difference in general availablity of ammo (especially now). Do these calibers share any uses such as coyote hunting, or other small game. What I am really after in all this is--how do these rounds differ in performance? Thanks