One of many articles on the subject
http://www.humanevents.com/2011/02/15/223-remington-vs-556-nato-what-you-dont-know-could-hurt-you/
So basically its just a thicker interior casing on the 5.56 to hold a bigger charge.
Question still is : do you need different dies?
Sent From Cr0ck1' IPhone most likely from the woods.
5.56 is loaded to NATO specs and pressures @ 61,000 psi.
223 Rem is loaded to SAAMI specs @ 55,000 psi.
You do not need different dies to load the 5.56, the difference is mainly in the chamber throat of the barrel. One problem you will encounter if you try to re-load nato brass, is the primer crimp. It's a bear to punch the primer out, then you need to remover the crimp from the primer pocket.
If your gun is marked 5.56 your safe to shoot 223 and 5.56. If your gun is marked 223 it's recommended not to shoot 5.56 ammo.
http://en.wikipedia.org/wiki/.223_Remington
read that...learn ya self sumtin....lol
