The 5.56×45mm NATO (official NATO nomenclature 5.56 NATO, commonly pronounced "five-five-six") is a rimless bottlenecked centerfire intermediate cartridge family developed in the late 1970s in Belgium by FN Herstal. It consists of the SS109, L110, and SS111 cartridges. On 28 October 1980, under STANAG 4172, it was standardized as the second standard service rifle cartridge for NATO forces as well as many non-NATO countries. Though they are not identical, the 5.56×45mm NATO cartridge family was derived from the .223 Remington cartridge designed by Remington Arms in the early 1960s, which has a near-identical case. However, firing chamber dimensions differ slightly between rifles manufactured for the designated cartridges. The differences may cause unsafe chamber pressures when firing 5.56 NATO in rifles designed for .223 Remington. Therefore, this combination is not recommended.
History
In 1954, the larger 7.62×51mm NATO rifle cartridge was selected as the first standard NATO rifle cartridge. At the time of selection, there had been criticism that the recoil power of the 7.62×51mm NATO, when fired from a handheld lightweight modern service rifle in full automatic mode, did not allow for sufficient control, so the automatic follow-on shots would not hit the intended target but scatter around it.
The British had extensive evidence from their own experimentation with intermediate cartridges since 1945, and were on the point of adopting the .280 (7 mm × 43mm) cartridge when the selection of 7.62×51mm (.308) as the NATO standard was made. The FN company had also been involved in the development of the .280 round, including developing a version of the FN FAL in .280. The United States overruled concerns about the recoil and overall effectiveness of 7.62 mm, and the other NATO nations accepted that standardization was more important than the selection of a cartridge that was otherwise ideal.
The development of the cartridge that eventually became the .223 Remington (from which 5.56mm NATO would eventually be developed) would be intrinsically linked to the development of a new lightweight combat rifle. The cartridge and rifle were developed as a single unit by Fairchild Industries, Remington Arms, and several engineers working toward a goal set by the U.S. Continental Army Command (CONARC). Early development work began in 1957. A project to create a small-calibre, high-velocity (SCHV) firearm was created. Eugene Stoner of ArmaLite was invited to scale down the AR-10 (7.62mm) design. Winchester was also invited to participate. The parameters that were requested by CONARC:
Springfield Armory's Earle Harvey lengthened the .222 Remington cartridge case to meet the requirements. It was then known as the .224 Springfield. Concurrently with the SCHV project, Springfield Armory was developing a 7.62mm rifle. Harvey was ordered to cease all work on the SCHV to avoid any competition for resources.
Eugene Stoner of Armalite (a division of Fairchild Industries) had been advised to produce a scaled-down version of the 7.62mm AR-10 design. In May 1957, Stoner gave a live-fire demonstration of the prototype of the AR-15 for General Willard G. Wyman, Commander-in-Chief of CONARC. As a result, CONARC ordered rifles to test. Stoner and Sierra Bullet's Frank Snow began work on the .222 Remington cartridge. Using a ballistic calculator, they determined that a 55-grain bullet would have to be fired at to achieve the 500-yard performance necessary.
Robert Hutton (technical editor of Guns & Ammo magazine) started development of a powder load to reach the goal. He used DuPont IMR4198, IMR3031, and an Olin powder to work up loads. Testing was done with a Remington 722 rifle with a 22-inch Apex barrel. During a public demonstration, the round successfully penetrated the U.S. steel helmet as required. But testing showed that chamber pressures were excessively high.
Stoner contacted both Winchester and Remington about increasing the case capacity. Remington created a larger cartridge called the ".222 Special", which was loaded with DuPont IMR4475 powder. During parallel testing of the T44E4 (future M14) and the AR-15 in 1958, the T44E4 experienced 16 failures per 1,000 rounds fired compared to 6.1 for the AR-15.
Due to several different .222-caliber cartridges being developed for the SCHV project, the .222 Special was renamed .223 Remington in 1959. In May of that year, a report found that five- to seven-man squads armed with AR-15 rifles had higher hit probabilities than 11-man squads armed with M-14 rifles. At a picnic, Air Force General Curtis LeMay fired an AR-15 and was very impressed with it. He ordered a number of them to replace M2 carbines that were in use by the Air Force. By November, testing at Aberdeen Proving Ground showed that the AR-15 failure rate had declined to 2.5 failures per 1,000 rounds, resulting in the M-16 being approved for Air Force Trials.
Marksmanship testing in 1961, comparing the M-16 to the M-14, indicated that 43% of M-16 shooters achieved "expert," while only 22% of M-14 shooters did. General LeMay subsequently ordered 80,000 rifles.
In the spring of 1962, Remington submitted the specifications of the .223 Remington to the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI). In July 1962, operational testing ended with a recommendation for adoption of the M-16 rifle chambered in .223 Remington.
In September 1963, the .223 Remington cartridge was officially accepted and named "Cartridge, 5.56mm ball, M193". The specification includes a Remington-designed bullet and the use of IMR4475 powder which resulted in a muzzle velocity of and a chamber pressure of 52,000 psi.
In 1970, NATO members signed an agreement to select a second, smaller caliber cartridge to replace the 7.62×51mm NATO cartridge. Of the cartridges tendered, the .223 Remington (M193) was the basis for a new design created by FN Herstal. The FN-created cartridge was named "5.56×45mm NATO" with a military designation of SS109 in NATO and M855 in the U.S. These new SS109 ball cartridges required a 228 mm (1-in-9 inch) twist rate while adequately stabilizing the longer L110 tracer projectile required an even faster, 178 mm (1-in-7 inch), twist rate.
The Belgian 62 gr SS109 round was chosen for standardization as the second NATO standard rifle cartridge which led to the October 1980 STANAG 4172. The SS109 used a 62 gr full metal jacket bullet with a seven grain mild steel tip to move the center of gravity rearward, increasing flight stability and thereby the chances of striking the target tip-first at longer ranges, in part to meet a requirement that the bullet be able to penetrate through one side of a WWII U.S. M1 helmet at 500 yd (457 m) (which was also the requirement for the 7.62×51mm NATO). An actual helmet was not used for developmental testing; instead, an SAE 1010 or SAE 1020 mild steel plate was positioned to be struck at exactly 90 degrees. It had a slightly lower muzzle velocity but better long-range performance due to higher sectional density and a superior drag coefficient.
The .223 Remington cartridge inspired an international tendency toward relatively small-sized, lightweight, high-velocity military service cartridges that allow a soldier to carry more ammunition for the same weight compared to their larger and heavier predecessor cartridges, have favourable maximum point-blank range or "battle zero" characteristics, and produce relatively low bolt thrust and free recoil impulse, favouring lightweight arms design and automatic fire accuracy.
Cartridge dimensions
The 5.56×45mm NATO has a 1.85 mL (28.5 gr H2O) cartridge case capacity.
5.56×45mm NATO maximum NATO cartridge dimensions, all sizes in millimeters (mm)NATO EPVAT testingQuickLOAD
The rifling twist rate for this cartridge is 177.8 mm (1 in 7 in.), 6 grooves right-hand twist, Ø lands = , Ø grooves = .
According to STANAG 4172 and the official NATO proofing guidelines, the 5.56×45mm NATO case can handle up to piezo service pressure. In NATO-regulated organizations, every rifle cartridge combination has to be proofed at to certify for service issue. STANAG 4172 defines the Belgian ball cartridge SS109 as the NATO reference cartridge and adds a considerable number of technical requirements like a minimum pressure of at the gas port down the long standard proof barrel and primer sensitivity that are not defined by civilian C.I.P. and SAAMI ammunition rulings and recommendations.
The NATO military alliance uses a NATO-specific recognized class of procedures to control the safety and quality of firearms ammunition called NATO EPVAT testing. The civilian organisations C.I.P. and SAAMI use less comprehensive test procedures than NATO. The NATO Manual of Proof and Inspection AC/225 (LG/3-SG/1) D/8 stipulates each weapon and component considered vulnerable to the effects of a rapid change in pressure, for example barrels, breech blocks and bolts, will be tested by firing one dry round at a corrected minimum of 25% over pressure and one oiled round at a corrected minimum of 25% over pressure. Over pressure of 25% means 25% in excess of the service pressure resulting from the 5.56×45mm NATO up to (Pmax) piezo service pressure. The service pressure is defined as the mean pressure generated by the service cartridge at a temperature of . Such a high-pressure proof is conducted with both the weapon and ammunition conditioned to an ambient temperature of . Each weapon will be individually tested using an ammunition lot that meets a minimum corrected mean chamber pressure. The corrected proof pressure requirement (service pressure (Pmax) + 25%) for the 5.56×45mm NATO like the STANAG 4172 is (PE) piezo pressure. This pressure has to be recorded in a NATO-design EPVAT barrel with Kistler 6215 transducer, HPI GP6 Transducer or by equipment to C.I.P. requirements.
The US SAAMI lists maximum average pressure (MAP) for the .223 Remington cartridge as piezo pressure with deviation of up to .
Rifle barrel configurations When 5.56×45mm NATO was adopted as standard in 1980, NATO chose a 178 mm (1:7) rifling twist rate for the 5.56×45mm NATO chambering to adequately stabilize the relatively long NATO L110/M856 5.56×45mm NATO tracer projectile. The US at that time converted all rifles in inventory by replacing the barrels and all new US military rifles since have been manufactured with this ratio.
In the US, builders of AR-type rifles can specify barrels with either .223 Remington, .223 Wylde, 223 Noveske, or 5.56×45mm NATO chambers in lengths from pistol (7.5") to long rifle (24"). These barrels are also available with rifling ranging from 356 mm (1-in-14") to 178 mm (1-in-7"). US makers are moving toward 5.56×45mm NATO and 178 mm (1-in-7"), which will ensure the least liability. Those chambered for .223 Remington may not have a fast enough rifling to stabilize the longer 5.56×45mm NATO bullets, which range up to 77 gr. Some hunting loads of .223 Remington go to 90 grains.
Performance
The 5.56×45mm NATO SS109/M855 cartridge (NATO: SS109; U.S.: M855) with standard 62 gr. lead core bullets with steel penetrator will penetrate about into soft tissue in ideal circumstances. As with all spitzer shaped projectiles, it is prone to yaw in soft tissue. However, at impact velocities above roughly , it may yaw and then fragment at the cannelure (the crimping groove around the cylinder of the bullet). These fragments can disperse through flesh and bone, inflicting additional internal injuries.
Fragmentation, if and when it occurs, imparts much greater damage to human tissue than bullet dimensions and velocities would suggest. This fragmentation effect is highly dependent on velocity and therefore on barrel length: short-barreled carbines generate lower muzzle velocity and therefore lose wounding effectiveness at much shorter ranges than longer-barreled rifles.