223 is not NATO 7.62, it is NATO 5.56.
Technically, the .223 is not a NATO 5.56. The differences are in the “ledde” in the chamber and there is more wall thickness in the .5.56. Externally they are the same and will interchange although some firearm manufacturers don’t approve of it.
http://www.humanevents.com/2011/02/15/223-remington-vs-556-nato-what-you-dont-know-could-hurt-you/
I agree, and the same notion applies between 308 Win and 7.62x51 NATO.