The .223 Remington has 1.87 ml
H2O) cartridge case capacity. .223 Remington maximum C.I.P. cartridge dimensions
. All sizes in millimeters (mm).
Americans would define the shoulder angle at alpha/2 = 23 degrees. The common rifling
twist rate for this cartridge is 305 mm (1 in 12 in), 6 grooves, Ø lands = 5.56 millimetres (0.219 in), Ø grooves = 5.59 millimetres (0.220 in), land width = 1.88 millimetres (0.074 in) and the primer type
is small rifle.
According to the official Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives
(C.I.P.) guidelines the .223 Remington case can handle up to 430 megapascals (62,366 psi) piezo pressure. In C.I.P. regulated countries every rifle cartridge combo has to be proofed
at 125% of this maximum C.I.P. pressure to certify for sale to consumers. This is equal to the NATO maximum service pressure guideline for the 5.56x45mm NATO
The SAAMI pressure limit for the .223 Remington is set at 379.212 megapascals (55,000 psi), piezo pressure.  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 38 to 55 grains (2.5 to 3.6 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-9, or 1-in-8. (Most modern AR-15s use 1-in-9 which is suitable for bullets up to 69 grains / 4.5 grams 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 / 3.6 grams.) The semi-automatic rifle category is often used by law enforcement, for home defense, and for varmint hunting. 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 "service rifle" category or 3 gun matches.  .223 Remington versus 5.56 mm NATO
These 5.56x45mm NATO
cartridges are identical in appearance to .223 Remington. They are, however, not completely interchangeable.
While the 5.56mm NATO
and .223 Remington cartridges and chamberings are very similar, they are not identical.
Military cases are generally made from thicker brass than commercial cases; this reduces the powder capacity (an important consideration for handloaders
), and the NATO specification allows a higher chamber pressure. NATO EPVAT
test barrels made for 5.56mm NATO measure chamber pressure at the case mouth, as opposed to the location used by the United States civil standards organization SAAMI. The piezoelectric sensors
or transducers NATO and SAAMI use to conduct the actual pressure measurements also differ. This difference in measurement method accounts for upwards of 137.9 megapascals (20,000 psi) difference in pressure measurements. This means the NATO EPVAT maximum service pressure of 430 megapascals (62,000 psi) for 5.56mm NATO, is reduced by SAAMI to 379.21 megapascals (55,000 psi) for .223 Remington.
In contrast to SAAMI, the other main civil standards organization C.I.P.
defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56mm NATO.
The 5.56mm NATO chambering, known as a NATO or mil-spec chamber, has 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 Remington chambering, known as 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 (Rock River Arms)
or the ArmaLite
chamber, which are designed to handle both 5.56mm NATO and .223 Remington equally well. The dimensions and leade of the .223 Remington minimum C.I.P. chamber also differ from the 5.56mm NATO chamber specification.
Using commercial .223 Remington cartridges in a 5.56mm NATO chambered rifle should work reliably, but generally will not be as accurate as when fired from a .223 Remington chambered gun due to the longer leade.
Using 5.56mm NATO mil-spec cartridges (such as the M855) in a .223 Remington 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 5.56mm NATO, 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 5.56mm NATO ammunition.