5.56 x 45 mm NATO
Encyclopedia : 5 : 55 : 556 : 5.56 x 45 mm NATO
5.56 × 45 mm NATO, designated STANAG 4172, is the standard rifle ammunition for NATO forces. It is derived from, but not entirely interchangeable with, the .223 Remington cartridge.
History
The previous standard NATO round was the 7.62 × 51 mm, derived from the .300 Savage rifle cartridge and designed to replace the U.S. military's .30-06 Springfield rifle cartridge. At the time of selection, there had been criticism that the 7.62 mm round was too powerful for modern assault rifles often causing excessive recoil, and smaller alternatives had been tendered. These doubts would later be shown to be well-founded.
During the late 1950s, ArmaLite and other U.S. firearm designers started their individual Small Caliber/High Velocity (SCHV) assault rifle experiments using the commercial .222 Remington cartridge. When it became clear that there was not enough powder capacity to meet U.S. Continental Army Command's (CONARC) velocity and penetration requirements, ArmaLite contacted Remington to create a similar cartridge with a longer case body and shorter neck. This became the .222 Remington Special. At the same time, Springfield Armory's Earle Harvey had Remington create an even longer cartridge case then known as the .224 Springfield. Springfield was forced to drop out of the CONARC competition, and thus the .224 Springfield was later released as a commercial sporting cartridge known as the .222 Remington Magnum. To prevent confusion with all of the competing .222 cartridge designations, the .222 Remington Special was renamed the .223 Remington. After playing with their own proprietary cartridge case design, the .224E1 Winchester, Winchester eventually standardized their case dimensions, but not overall loaded length, with the .222 Remington Special to create a cartridge known as the .224E2 Winchester. With the U.S. military adoption of the ArmaLite AR-15 as the M16 rifle in 1963, the .223 Remington was standardized as the 5.56 × 45 mm. However, the .223 Remington was not introduced as a commercial sporting cartridge until 1964.
During the 1970s, NATO members signed an agreement to select a second, smaller caliber cartridge to replace the 7.62 mm NATO. Of the cartridges tendered, the 5.56 mm was successful, but not the 5.56 mm loading (M193 Ball) as used by the U.S. at that time. Instead, the Belgian FN SS109 loading was chosen for standardization. The SS109 used a heavier bullet at a lower muzzle velocity for better long-range performance, specifically to meet a requirement that the bullet be able to penetrate through one side of a steel helmet at 600m. Some believe that this requirement has made the M855 less capable of fragmentation than the M193 as discussed below.
The cartridge is 57 mm (approximately 2.25 inches) long and 9.7 mm (0.38 inches) in diameter. The bullet itself is 20 mm (0.75 inches) long and 5.7 mm (0.224 inches) in diameter.
The .223 Remington cartridge has the same dimensions as the 5.56 × 45 mm, but (generally) has a lower propelling charge, the NATO loading being the more powerful. Chambering and firing a 5.56 × 45 mm round in a .223 rifle is possible, but not always wise. However, it is safe, if not always effective, to fire a .223 Remington round from firearms designed for the 5.56 mm. Certain commercial firearms manufacturers, including Bushmaster Firearms, specifically design their products to be able to fire either load interchangeably, or even as alternating rounds in the same magazine.
Performance
The 5.56 × 45 mm NATO cartridge with the standard military ball bullet (NATO: SS109; U.S.: M855) will penetrate approximately 15 to 20 inches (380 to 500 mm) 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 2,700 ft/s (820 m/s), it will yaw and then fragment at the cannelure (the groove around the cylinder of the bullet). The fragments disperse through the flesh causing much more internal injury. The effectiveness of fragmentation seems to impart much greater damage to tissue than bullet dimensions and velocities would suggest. This fragmentation effect is highly dependent on velocity, and therefore barrel length: short-barreled rifles generate less muzzle velocity and therefore rounds lose effectiveness at much shorter ranges than longer-barreled rifles.
Separately, hydrostatic shock is often cited as a primary wounding or incapacitation mechanism in high-velocity projectiles like 5.56 mm NATO, though this has been conclusively disproven.
There has been much criticism of the poor performance of the round, especially the first-round kill rate when using firearms that don't achieve the velocity to cause fragmentation. Typically, this only becomes an issue at longer ranges (over 100 meters) or as already stated with shorter barreled weapons. The 14.5-inch barrel of the U.S. military's M4 Carbine can be particularly prone to this problem. At short ranges, the round is extremely effective, and its tendency to fragment reduces the risk to bystanders when used inside a building or in an urban environment — the bullet fragments, remaining in the target. By comparison, larger pistol-caliber bullets pose a far greater threat of passing through the target and causing additional casualities.
However the small round simply does not do enough damage when unfragmented, assuming a critical area is not hit, to incapacitate a human reliably with a single shot. Barrier performance (i.e. shooting through materials) is also relatively poor (although even the 7.62 mm NATO round is not particularly effective through vehicles) partly because the light and fast bullet is easily deflected.
Recently, huge advances have been made in 5.56 mm ammunition. The US military has adopted for limited issue a 77-grain "Match" bullet, type classified as the Mk 262. The heavy, lightly constructed bullet fragments more violently at short range and also has a longer fragmentation range. Originally designed for use in the Mk 12 SPR, the ammunition has found favor with special forces units who were seeking a more effective round to fire from their M4A1 carbines.
Another specialty round is M995, a penetrating round with a tungsten core designed for use in the M249 SAW and issued in linked belts. This round is designed exclusively for penetration, and according to Dr. Gary Roberts, an expert in terminal ballistics, it will easily pass through level III and IV body armor panels, both of which will stop conventional 5.56 mm and 7.62 mm bullets.
5.56 mm NATO vs. .223 Remington
In January 1979, the Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) advised that 5.56 x 45 mm military specification ammunition is generally not safe to fire in .223 Remington-chambered rifles (which are mainly civilian sporting rifles). [link] The chambers of weapons intended to take the NATO round are oversize relative to the civilian weapons to allow for greater variation in production (and hence reliability), and 'hotter' loads containing more propellant. By contrast, SAAMI-specification chambers are manufactured tighter (for accuracy), and 5.56 mm NATO ammunition, at the larger end of the manufacturers' tolerances, will be too tight and result in overpressure. This can cause excessive wear, or even theoretically cause parts of the rifle to rupture. Conversely, civilian .223 ammunition is perfectly safe to use in military rifles.[link]
Comparison of 5.56 mm vs. 7.62 mm NATO
| Round | Cartridge size | Bullet weight | Velocity | Energy |
|---|---|---|---|---|
| 5.56 mm NATO | 5.56 × 45 mm | 3.95–5.18 g | 772–930 m/s | 1,700–1,830 J |
| 7.62 mm NATO | 7.62 × 51 mm | 9.33 g | 838 m/s | 3,275 J |
The NATO Ball round (U.S.: M855) can penetrate up to 3 mm of steel, while the Armor-Piercing variant (U.S.: M995) can penetrate up to 6 mm.
Use
Many nations besides those that are members of NATO use the 5.56 mm NATO cartridge, and equally a number of manufacturers produce weapons in this calibre. Outside of the NATO members there are the following weapons:
- Australian F-88 Austeyr assault rifle
- Belgian FN FNC assault rifle
- Indian INSAS assault rifle
- Israeli IMI Negev, Galil assault rifle and Tavor TAR-21 bullpup assault rifle
- Japanese Type 89 Assault rifle with lesser performance Type 89 cartridge
- Russian AK-101 and AK-108
- Singaporean SAR-21
- South African Vektor R4 and R5
- South Korean K-2 (rifle)
- Swedish Ak 5 system, derived from the Belgian FN FNC assault rifle
- Swiss SIG 550 with lesser performances than the round for which it was built: the Gw Pat.90 cartridge
- Remington Model 7615 Police Patrol Rifle
- Remington Model 700 series bolt-action rifle.
- Winchester Model 70 series bolt-action rifle.
- Steyr Scout series bolt-action rifle.
- Ruger Mini-14 semi-automatic rifle
See also
Sources & external links
- [FAS: 5.56 mm Ammunition]
- [The Gun Zone: 5.56 mm FAQ]
- [The Gun Zone: A 5.56 mm Timeline]
- [I.M.I Small Arms Ammunition Division]
- [The AR-15.COM Ammo-Oracle]
- [Nazarian`s Gun`s Recognition Guide]
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