Is there not a difference in the throating. Without checking reference books, I seem to remember that the 5.56 NATO has a longer throat than the 223 Remington, similar to the Weatherby chamberings.
That's my understanding -- longer throat and maybe a bit larger diameter in the neck portion of the chamber. The common advice (and I think this comes from SAAMI) is not to run 5.56 ammo in a .223 chamber. There are also some other chamber configurations, such as the Wylde chamber, that are supposed to allow the use of both rounds without the theoretical loss in accuracy you get when running .223 in at 5.56 chamber.
I'm skeptical about the 60k figure being CUP, but I have read that in more than one source, albeit hearsay. I don't know. And, my suspicion is that the reason for the crimped primers has nothing to do with pressures standards either.
There's BS on the internet??
A friend of mine once commented that he doesn't believe anything unless he sees it himself, and even then, he only believes about half of what he sees!
