.223 Remington

.223 Remington
.223 Rem (left) next to .30-30 (center) and .308 (right)
Type	Rifle/varmint
Country of Origin	United States
Specifications
Parent Case	.222 Remington Magnum
Case Type	Rimless, bottleneck
Bullet Ø	.224 in (5.7 mm)
Neck Ø	.253 in (6.4 mm)
Shoulder Ø	.354 in (9.0 mm)
Base Ø	.376 in (9.6 mm)
Rim Ø	.378 in (9.6 mm)
Rim Thickness	.045 in (1.1 mm)
Case Length	1.76 in (45 mm)
Full Length	2.26 in (57 mm)
Rifling twist	1/12" (typical)
Primer	Small rifle
Production & Service
Designer	Remington Arms
Design Date	1964
Production Dates	1965-present
Variants	.223 Ackley Improved, 5.56x45mm NATO
Ballistic Performance Sampling
Bullet Wt./type Velocity Energy 36 gr (2.3 g) JHP 3,750 ft/s (1,140 m/s) 1,124 ft·lbf (1,524 J) 55 gr (3.6 g) Nosler ballistic tip 3,240 ft/s (990 m/s) 1,282 ft·lbf (1,738 J) 60 gr (3.9 g) Nosler partition 3,160 ft/s (960 m/s) 1,330 ft·lbf (1,800 J) 69 gr (4.5 g) BTHP 2,950 ft/s (900 m/s) 1,333 ft·lbf (1,807 J) 77 gr (5.0 g) BTHP 2,750 ft/s (840 m/s) 1,293 ft·lbf (1,753 J) Test barrel length: 24 in.>br/>Source: Federal Cartridge

The .223 Remington is a sporting cartridge with the same external dimensions as the 5.56x45mm NATO military cartridge. It is loaded with a 0.224-inch (5.7 mm) diameter, jacketed bullet, with weights ranging from 40 up to 90 grains (5.8 g), though the most common loading by far is 55 grains (3.6 g).

While the external case dimensions are very similar, the .223 Remington and 5.56x45mm differ in both maximum pressure and chamber shape. The maximum and mean pressures for some varieties the 5.56 mm (different cartridge designations have different standards) exceed the SAAMI maximums for the .223 Remington, and the methods for measuring pressures differ between NATO and SAAMI. The 5.56 mm chamber specification has also changed over time since it's adoption, as the current military loading (NATO SS-109 or US M855) uses longer, heavier bullets than the original loading did. This has resulted in a lengthening of the throat in the 5.56 mm chamber. Thus, while .223 Remington ammunition can be safely fired in a 5.56 mm chambered gun, firing 5.56 mm ammunition in a .223 Remington chamber may produce pressures in excess of even the 5.56 mm specifications due to the shorter throat.

History

The .223 Remington was developed as an enlarged and higher velocity version of the .222 Remington, which was introduced in 1950 as a varmint cartridge. The .223 Remington was developed specifically for the Armalite AR-15, a version of which later became the U.S. military's M16 rifle.

Uses

The .223 Remington is one of the most common rifle cartridges in use in the United States, being widely used in two types of rifles: (1) varmint rifles, most of which are bolt action and commonly have 1-in-12 rifling twist suitable for bullets between 40 and 60 grains (3.9 g), and (2) semi-automatic rifles such as the AR-15 and the Ruger Mini-14, which are commonly found to have twist rates of 1-in-7, 1-in-12, or 1-in-9. (Most modern AR-15s use 1-in-9 which is suitable for bullets up to 75 grains (4.9 g) or 1-in-7 which is suitable for slightly heavier bullets, but older AR-15s used 1-in-12 twist rates, making them suitable for use with bullets of 55 grains.) The semi-automatic rifle category is often used by law enforcement, for home defense, and for varmint hunting (especially farm and ranch work, after which Ruger named a version of its Mini-14 the "Ranch Rifle"). Among the many popular modern centerfire rifle cartridges, .223 Remington ammunition is among the least expensive and is often used by avid target shooters, particularly in the "high power rifle" category.

.223 Remington versus 5.56 mm NATO

Dimensions of a .223 Remington cartridge

While the 5.56 mm and .223 cartridges are very similar, they are not identical. Military cases are made from thicker brass than commercial cases, which reduces the powder capacity (an important consideration for handloaders), and the NATO specification allows a higher chamber pressure. Test barrels made for 5.56 mm NATO measure chamber pressure at the case mouth, as opposed to the SAAMI location. This difference accounts for upwards of 20,000+ psi difference in pressure measurements. That means that advertised pressure of 58,000 psi for 5.56 mm NATO, is around 78,000 psi tested in .223 Rem test barrels (SAAMI .223 Rem Proof MAP is 78,500 psi so every 5.56 mm round fired is a proof load, very dangerous). The 5.56 mm chambering, known as a NATO or mil-spec chambers, have a longer leade, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 chambering, known as the "SAAMI chamber", is allowed to have a shorter leade, and is only required to be proof tested to the lower SAAMI chamber pressure. To address these issues, various proprietary chambers exist, such as the Wylde chamber or the Armalite chamber, which are designed to handle both 5.56 mm and .223 equally well.

These 5.56x45mm NATO cartridges are identical in appearance to .223 Remington. They are, however, not completely interchangeable.

Using commercial .223 cartridges in a 5.56-chambered rifle should work reliably, but generally will not be as accurate as when fired from a .223-chambered gun due to the excessive lead. Using 5.56 mil-spec cartridges (such as the M855) in a .223-chambered rifle can lead to excessive wear and stress on the rifle and even be unsafe, and the SAAMI recommends against the practice. Some commercial rifles marked as ".223 Remington" are in fact suited for 5.56 mm, such as many commercial AR-15 variants and the Ruger Mini-14, but the manufacturer should always be consulted to verify that this is acceptable before attempting it, and signs of excessive pressure (such as flattening or gas staining of the primers) should be looked for in the initial testing with 5.56 mm ammunition.

Related cartridges

P.O. Ackley created an improved version of this cartridge called the .223 Ackley Improved. It has the straight sides and steep shoulder typical of the Ackley design improvements, yielding about 5% extra case volume. This in turn provides longer case life, less stretching, and up to 100 ft/s (30 m/s) faster velocities.

Wildcat cartridge developers have long necked this cartridge up to create the 6mm/223 or 6x45. At one time this round was very popular for varminting and competition but has been replaced by current popular competition cartridges using short fat cases, such as the 6 mm PPC and the 6 mm BR Remington.

See also

• List of rifle cartridges
• 5 mm caliber
• Delta L problem

External links

• .223 Remington Cartridge Guide by AccurateShooter.com
• AR15 Ammo Oracle by Troy Tiscareno
• A 5.56x45mm "Timeline" by Daniel Watters