Its 5.56 Nato which is the same as .223 inch just like 7.62(7.62X 51) Nato is the same as .308 (7.62X51) different for 7.62X "39" different case size for the AK/ sks crowd.
Pays to KNOW what is up/down when the $hit goes round. Don'tcha know.
5.56 NATO is not exactly the same as .223 Remington just as 7.62 NATO is not the same as .308 Win. They are often close enough but in match chambers you will notice the difference.