Jeremy said:
5,56 brass is thicker and more straight lined. A nato round can be made in just about any country on any machine that will form casimgs technically it's easier to keep the brass fustionable and withing safe firing specs at the case neck if it's a straight angle rather than a rounded "blown out" shoulder. Inherently a rifle chanbered for 5.56 nato has a bigger chanber to account for the differences in ammo tolerances. Which can cause a problem if you get a bad .223 rem round. The bigger 5.56 chamber doesn't hold a 223 round as tightly and the thinner brass in the 223 can stretch and blow apart . Not a common malfuction but it does happen. Until recent years the 556 was loaded faster. With the thicker brass and different chamber and throat it could be loaded hotter without increasing the pressure to unsafe ranges. While yes the rounds for 556 can splinter that's usuallty the jacket seperating from the steel core but as far as more lethal that a 50/50 There is also the arguement that the 556 was designed to wound rather than kill imediatly for the simple fact that a dead soldier takes only 1 person out of battle while a seriously wounder solder takes 3 out of battle; the guy hit and the 2 guys to carry him out of the engagement zone. You pick decide which makes more sense
If you really want to know I can explain the differences between the 2 in detail for you but it's to much to type in here. They can be very different rounds. To be safe shoot only ammo that matches the gun 556 in 556 and 223 in 223 1 bad casing can really ruin your day.
And the same malfunction could happen in a .223 rifle with the same bad round so that kind of negates your point here.
If you are getting an AR, ALWAYS have it chambered in 5.56. I can't think of any damned reason why you wouldn't want it chambered in 5.56. This excludes match grade barrels, some of them are .223 only but i'd try to find a 5.56 one if possible. The NATO round is a higher pressure round, hence the flatter ballistics and the splintering on impact.