Guns: 5.56 NATO

More so than most other rounds, the 5.56x45mm rifle cartridge is associated with a single country (the U.S.). Indeed, the fortunes of 5.56 NATO and the U.S. Armed Force's M16 have been forever linked, even though other nations' rifles fire the 5.56 cartridge and other calibers have been introduced for AR-type rifles. Part of this is simple geography - while you can find 7.62x39-chambered AKs and SKSs in almost every Third World mudhole, from Colombia to Darfur to Kosovo to East Timor, I'd wager that the majority of 5.56mm rifles are in the hands of U.S. civilians in the form of semiautomatic AR-15s.

The cartridge itself is an unassuming little thing, and its overall diameter will probably surprise people who might expect something bigger from the primary infantry weapon of the most advanced military in history. There have been many supporters and detractors of the 5.56mm over the years (step over to the AR-15 Ammo Oracle for more info than you can shake a stick at), but it's definitely been rising in popularity over the past couple decades. In my opinion, for ranges up to about 200 yards, a 5.56-chambered carbine will do about as well as anything available right now.

One big problem, though, is supply. Since many militaries use 5.56 NATO, high prices and absurdly limited supply are sometimes the norm. I remember when you could get a case of XM193 surplus for $130 - those days are LONG gone. In a pinch, though, I suppose you could use commercial softpoint hunting ammo for your AR. The velocity is going to be quite different, and the gun may cycle differently, but at least you'll have something to shoot.