When folks say, "Mr. Eatman," I look over my shoulder to see if my father's standing there...
As near as I can tell, the .223/5.56 thing has to do with the length and shape of the bullet, comparing civilian and military. It is said that the length, and the shape of the ogive, for the military round might have the bullet just touching the lands of a civilian rifle. Military chambers apparently have a smidgen more freebore in front of the chamber than is found in a civilian rifle.
The fear is that there could be higher than desirable pressures with the bullet touching the lands--again, this is a "near as I can tell" thing. However, many people find their best accuracy when the bullet is very, very close to the lands.
Anecdote: I mis-seated some .243 loads, one time, where the bullets weren't far enough into the neck. They shot beautiful groups, but when I went to unload the rifle the bullet stayed stuck in the start of the lands. So, I guess that's why I've never worried about .223/5.56 "problems".
Be that as it may, folks oughta stay with what they think is right for them. For all I know, I'm surviving on account of nothing more than dumb luck.
$0.02,
Art