I don't have the book handy so I'll have to check to be absolutely certain, but when Jack looks at the rifle cartridge he found, I get the impression that he sees a headstamp which says "5.56 NATO." (To distinguish it from the 223 Remington, which is exactly the same cartridge . . . dimensionally.) I've never seen such a headstamp. Mind you, I haven't seen every type of European or Asian round, but those I have seen almost invariably have a "manufacturers" headstamp. Even military rounds have the manufacturers headstamp. ("WCC" which stands for "Winchester Cartridge Corporation" is an example. "IMI" which stands for "Israeli Military Industries" is another.) And rounds made by either commercial or military manufacturers, which are loaded to military specifications, have a little symbol on the headstamp which indicates a military loading. This symbol is a circle with what amounts to a plus-sign inside it. These same cartridges are also sold commercially. So . . . instead of mentioning "5.56 NATO," you might mention that tiny symbol instead.
The "plus" sign extends all the way across the inside of the circle, both vertically and horizontally -- like a pie cut into four equal sections.
Ken V.