243winxb,
The "circle cross" is a "NATO design mark" and not a guarantee of NATO interoperability. It simply means that the ammunition is nominally the correct dimensions, however as DTIC has noted, this is no guarantee that one countries ammo will function in another countries weapons. The prohibition of using American M855 or M855A1 in a Brit L85 is a well known example of this.
There is a variation of a "cloverleaf cross" which is the NATO symbol for interoperability.
http://www.dtic.mil/ndia/2011smallar...Pellegrino.pdf
Jimro