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Refers to any rifle that fires a .223 round such as the colt m16, ruger mini-14, bushmaster rifles etc.

The .223 is closely related to it's metric 'cousin' the 5.56x45 descused later on. The .223 is the main cartrage used in an ar-15 rifle yet it can also be found in other types of sporting rifles. Usually used for hunting varments, the .223 has an at muzzle speed of around 2500 fps. The .223 is found equiped with a bullet normaly ranging from a 55 grain hp/jhp (which is used primarily for target practice) to an 80 grain hp/jhp (which is used primarily for match shooting).

The 5.56x45 NATO (North Atlantic Treaty Organization) caleber is very close to the .223 yet very diferent. In a standard ar-15 rifle, 5.56 NATO or .223 can be effectively used. However in most sporting rifles only the .223 is recomended for use. The main reason for this is the load. The 5.56 NATO round provides more power that it is too powerful for the .223 chambered gun to withstand for any type of prolonged use. Therefor 5.56 is better for use in any gas opperated/blowback action gun. Also the 5.56 round has a thicker caseing (because of the 'hotter' load) which is better for reloading (because of resistance to cracking).

The 5.56x45 NATO also has one other major use. The 5.56 NATO spec round is the cartrage used by not only the US forces but those encompassed in the NATO aliance. The ammo usually used as NATO is manufactured by Lake City Amunition in Independence, Missouri. Along with this amunition the army also uses the 7.62x51 (.308) which ...