The 6mm Advanced Rifle Cartridge (6×38mm), or 6mm ARC for short, is a 6 mm (.243) caliber intermediate

rifle cartridge A rifle cartridge is a firearm cartridge (firearms), cartridge primarily designed and intended for use in a rifle/carbine, or machine gun. Types Full-powered A full-powered cartridge is a rifle cartridge used interchangeably between servic ...

introduced by

Hornady Hornady Manufacturing Company is an American manufacturer of ammunition cartridges, components and handloading equipments, based in Grand Island, Nebraska. History Joyce W. Hornady began manufacturing bullets in the spring of 1949 with a .30 cal ...

in 2020, as a low-

recoil Recoil (often called knockback, kickback or simply kick) is the rearward thrust generated when a gun is being discharged. In technical terms, the recoil is a result of conservation of momentum, for according to Newton's third law the force requ ...

, high-

accuracy Accuracy and precision are two measures of ''observational error''. ''Accuracy'' is how close a given set of measurements (observations or readings) are to their ''true value''. ''Precision'' is how close the measurements are to each other. The ...

long-range cartridge, designed for use in the M16 platform at request of a specialized group within the U.S. DoD for its multipurpose combat rifle program. When compared to the military 5.56mm NATO platform, 6mm ARC is dimensionally incompatible regarding barrel, bolt and magazine components.

Design and performance

The

STANAG magazine A STANAG magazine or NATO magazine is a type of detachable firearm magazine proposed by NATO in October 1980. Shortly after NATO's acceptance of the 5.56×45mm NATO rifle cartridge, Draft Standardization Agreement ( STANAG) 4179 was proposed i ...

-length cartridge was designed for and makes use of 6 mm (.243 in)

very-low-drag bullet A very-low-drag bullet (VLD) is primarily a small arms ballistics development of the 1980s–1990s, driven by the design objective of bullets with higher degrees of accuracy and kinetic efficiency, especially at extended ranges. To achieve this, ...

s, which are known for their high

ballistic coefficient In ballistics, the ballistic coefficient (BC, ''C'') of a body is a measure of its ability to overcome air resistance in flight. It is inversely proportional to the negative acceleration: a high number indicates a low negative acceleration—the ...

s due to the high

sectional density Sectional density (often abbreviated SD) is the ratio of an object's mass to its cross sectional area with respect to a given axis. It conveys how well an object's mass is distributed (by its shape) to overcome resistance along that axis. Secti ...

with less drag and better

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

retention at extended ranges. This promotes greater terminal characteristics at longer distances without having to shift to a larger, heavier rifle platform than the AR-15. With the release in 2020, Hornady also launched three factory loads with bullet weights and advertised G1 ballistic coefficients of .512, .530 and .536 respectively. The 6mm ARC is a medium-power cartridge comparable to the

6.5mm Grendel The 6.5mm Grendel (6.5×38mm) is an intermediate cartridge jointly designed by British-American armorer Bill Alexander, competitive shooter Arne Brennan (of Houston, Texas) and Lapua ballistician Janne Pohjoispää, as a low-recoil, high- precis ...

, but with better ballistics thanks to the greater muzzle velocity achieved by using lighter 6 mm bullets and enough power to make use of the heavy 6 mm bullets. The 6mm ARC has almost comparable velocities and ballistic performance as the .243 Winchester and

6.5mm Creedmoor The 6.5mm Creedmoor designated as 6.5 Creedmoor by SAAMI, and as 6,5 Creedmoor by the C.I.P. is a centerfire rifle cartridge introduced by Hornady in 2007. It was developed by Hornady senior ballistics scientist Dave Emary in partnership with D ...

, but out of a compact length cartridge that, without having to deal with substantial

bolt thrust Bolt thrust or breech pressure is a term used in internal ballistics and firearms (whether small arms or artillery) that describes the amount of rearward force exerted by the propellant gases on the Bolt (firearms), bolt or Breechblock, breech of a ...

or breech pressure increase related drawbacks, has less recoil and fits into the standard AR-15 length actions. The ability to use a cartridge with this level of performance in an AR-15 platform and especially with high BC bullets within the constraint of magazine length limitations, make this cartridge an excellent choice for use in an AR-15.

SAAMI, C.I.P. and commercial data

In addition to the above comments, there is some confusion regarding the 6 mm ARC's performance. This is because loading data given in some manuals such as the ''11th Edition Hornady Reloading Manual'', for example, has two sets of data. The first set of data is loaded to the

SAAMI The Sporting Arms and Ammunition Manufacturers' Institute (SAAMI, pronounced "Sammy") is an association of American manufacturers of firearms, ammunition, and components. SAAMI is an accredited standards developer that publishes several A ...

maximum average pressure (MAP) of 52,000 psi (358.53 MPa), which is stated to be suitable for gas-operated firearms such as the AR-15 platform and its derivatives. The second set of data is loaded to a MAP of 62,000 psi (428.48 MPa), which is stated to be for use with

bolt action Bolt action is a type of manual firearm action that is operated by ''directly'' manipulating the turn-bolt via a bolt handle, most commonly placed on the right-hand side of the firearm (as most users are right-handed). The majority of b ...

guns such as the CZ 527. The Hornady manual states that this second set of data should not be used in gas-operated firearms. Due to the lower MAP, the performance of 6mm ARC ammunition loaded to 10,000 psi lower gas-gun pressures will, on average, be less than firearms loaded to bolt action pressures when using the same barrel length. When using shorter barrels, which are common on gas-guns, the difference will be even more pronounced. For example, the data in the Hornady 11th Edition Manual for an 18 in (457 mm)-barrelled AR-15 platform firearm was on average 200–300 ft/s (60–90 m/s) less than the data for the 24 in (610 mm)-barrelled CZ 527 bolt action rifle. Reloading data publications from and commercially offered ammunition in C.I.P. member states must comply with C.I.P. procedures, rulings and legislation. According to the official C.I.P. rulings the 6mm ARC can handle up to P_max 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 means that 6mm ARC chambered arms in C.I.P. regulated countries are currently (2025) proof tested at PE piezo pressure. For small arms ammunition for use in " non-NATO Chamber" weapons,

NATO The North Atlantic Treaty Organization (NATO ; , OTAN), also called the North Atlantic Alliance, is an intergovernmental organization, intergovernmental Transnationalism, transnational military alliance of 32 Member states of NATO, member s ...

has chosen to conform to the procedures as defined by the current C.I.P. legislation.

Compatibility with the AR-15

For an ordinary AR-15 rifle chambered for the .223 Remington/ 5.56mm NATO, a new

barrel A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden stave (wood), staves and bound by wooden or metal hoops. The word vat is often used for large containers ...

magazine A magazine is a periodical literature, periodical publication, print or digital, produced on a regular schedule, that contains any of a variety of subject-oriented textual and visual content (media), content forms. Magazines are generally fin ...

and bolt are required to convert to the 6mm ARC. The 6mm ARC utilizes the same bolt head size as the

, and 6.5mm Grendel-compatible AR-pattern

box magazine A magazine, often simply called a mag, is an ammunition storage and feeding device for a repeating firearm, either integral within the gun (internal/fixed magazine) or externally attached (detachable magazine). The magazine functions by holdi ...

s have also been used successfully with the 6mm ARC. The 6mm ARC therefore can also be a suitable chambering for shorter "mini-action"

bolt-action rifle Bolt action is a type of manual firearm action that is operated by ''directly'' manipulating the turn-bolt via a bolt handle, most commonly placed on the right-hand side of the firearm (as most users are right-handed). The majority of b ...

s, such as the CZ 527 bolt action rifle mentioned previously. Depending on their case material and bullet weight, dimensionally similar 6.5mm Grendel cartridges weigh . That is significantly more when compared to 5.56mm NATO rounds.

The 6mm ARC as parent case

The relatively short, fat cartridge case is used as the parent case for other AR-15 compatible later cartridges, such as: * 22 ARC (2024) — a necked down 5.56 mm (.223) variant designed for very-low-drag bullets * 338 ARC (2025) — a necked up 8.6 mm (.338) (subsonic) variantSAAMI 338 Advanced Rifle Cartridge (338 AEC) drawing
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References

{{7.62×39derivatives Pistol and rifle cartridges

Design and performance

SAAMI, C.I.P. and commercial data

Compatibility with the AR-15

The 6mm ARC as parent case

See also

References