First off please verify whether or not I understand the differences between the 223 and 5.56 NATO correctly.
The 223 has thinner brass, slightly more case capacity, a shorter neck, loaded in the 50,000 cup range, generally loaded with 55gr or lighter bullets, barrels stamped “223” typically have a slower twist 1-12 rifling.
The 5.56 NATO has thicker brass, slightly less case capacity, a crimped in primer with a hard cup, a longer neck, loaded to higher 60,000 cup, generally loaded with 62+gr or heaver bullets, and barrels stamped “5.56” typically sport a faster twist 1-9 (or faster) rifling in order to stabilize the longer heaver bullets. Do I have that right?
When it comes to shooting “factory” ammo there is not that much to worry about, only the shooter should watch for signs of pressure and understand that their rifle will shoot best with the ammo marked the same as their barrel. Is this for the most part true?
The only real thing to worry about is the fact that 5.56 brass has less case capacity so using 223 load data could prove to be potentially dangerous. Of course a prudent handloader understands the importance of working up slowly, so this is an unlikely situation. Did I get that correct?
My next question is what sort of reloading dies do I need to load 5.56 ammo? Will 223 dies work seeing as external dimensions are virtually the same save for the longer neck, or do I need dies marked “5.56” for best results?