I'll admit that I'm looking forward to hearing Ridge elaborate on why he considers 223rem and 5.56 to be completely different animals, simply because I personally haven't taken interest in differentiating the two for myself. I've never owned a rifle chambered for a pure 223rem chamber, but alternatively, I haven't owned a piece of 5.56 ammo or brass in over a decade. All of my rifles are either 5.56 or 223 Wylde chambers, plus I only buy 223rem factory ammo and reload on 223rem brass.
its not the chambering, its the platform, you buy a bolt action 223, mout a scope and it sits around 1 1/2" off the axis of the barrel, but with an AR that's 3", that amounts to 15" of usable trajectory at 500 yards, then you have a faster 8 twist you use heavier bullets and boom, its a whole new cartridge. I hunted with that 788 remmy 223 for almost 20 years, then bought an RRA 8 twist varminter, though I killed thousands of groundhogs with it, the first year I had the RRA, I was averageing like 94 percent first round kills on groundhogs from 300 to 440 yards just using holdover. it was incredible. I managed 2 at 550 using 55 gr sp's when dialing, and busted rocks at 600 just to show folks what the lowly 223 firing 55 gr hunting ammo could do.
RR
an AR doesn't make a 223 what it ain't, but it makes it easier to use most of its potential.