The story of the 5.56x45mm NATO (.223 Remington) cartridge begins around 1950. At that time the US Army initiated the study of small arms effectiveness, that culminated in the famous ORO reports by Hall (An Effectiveness Study of the Infantry Rifle) and Hitchman (Operational Requirements for an Infantry Hand Weapon).
Among other conclusions, these reports called for a weapon with an effective range of about 300 yards, with controlled pattern dispersion of hits in bursts, to improve hit probability. One of the proposed solutions to the general problem of inaccuracy was to create a burst-firing small-caliber weapon firing a conventional projectile.
In 1952, an M2 carbine re-barreled to the experimental .22 caliber round (based on a shortened .222 Rem case) was studied and found promising. Various other rounds with .22 caliber projectiles, based on .30-06 and T67 (.30 / 7.62 NATO) were tested as well. In 1957, the Armalite Ar-15 rifle, firing the newly developed .222 remington Special cartridge was tested, and in 1959 the .222 Special cartridge, developed to fulfill new military requrements for 500 meters effective fire, was renamed to .223 Remington (as a commercial offering).
In 1961 the US Air Force and ARPA requested a number of .223 caliber Ar-15 rifles, and military service of the new round commenced in early 1962, when the US AF standardised the Stoner designed, Armalite AR-15 rifle as the M16. The US Army adopted the .223 cartridge as 5.56x45mm in 1963, and Remington commercially introduced the .223 as a hunting round in 1964.
Following the problems with the 7.62mm M14 rifle and protracted delays with the SPIW program, the M16 rifle and its .223 caliber (5.56×45) ammunition was adopted as the standard US Military infantry rifle system. After much field use in Vietnam and elsewhere, and extensive trials, an updated version of the .223 cartridge was officially adopted in 1979. It was loaded with the heavier SS109 (US designation M855) bullet of Belgian design. In 1954 the new 5.56x45mm caliber, became the standard NATO intermediate round. It would be known as 5.56x45mm NATO.
Recent issues with the insufficient stopping power of M855 5.56mm NATO ammunition in Iraq and Afghanistan (especially when firing from short-barrelled carbines) resulted in the development of an even heavier loading, the Mk.262. This was with a bullet of enhanced ballistic and striking performance.
Many other types of projectiles are also available for this caliber in ‘military’ versions, ranging from blank and short-range target practice rounds, up to armour-piercing and tracer. The variety of civilian versions (intended for small-game hunting, plinking, target shooting and self-defense) is almost infinite, and this round is produced in many countries. A great many weapons, both military and civilian, are available for this caliber.
|Designation||Bullet weight, g||Muzzle velocity, m/s||Muzzle energy, J||Comments|
|5.56×45 M193||3.5||991||1750||from standard assault rifle barrel (20″)|
|5.56×45 M885||4.15||930||1790||from standard assault rifle barrel (20″)|
|5.56×45 M885||4.15||880||1600||from carbine barrel (14″)|
|5.56×45 Mk.262||5||895||2000||from standard assault rifle barrel (20″)|
|5.56×45 Mk.262||5||772||1490||from carbine barrel (14″)|