I'm only asking because I'm looking for a simple way to explain it.
No such animal.
Chambering in a specific cartridge; not caliber.
New thread here the other day:
and links to this (which is fairly indepth look at your question):
And there is a physically observable difference between the .357 remington mag and .38 special example, whereas there is not necessarily such a difference between 5.56 and .223.
I just read the barrel and load accordingly regarding .223 remington and 5.56 NATO.