6mm ARC

6mm Advanced Rifle Cartridge
Rifle cartridges (l. to r.) .308 Win, 6mm ARC, 300 AAC, .223 Rem
Type	Centerfire rifle
Place of origin	United States
Production history
Manufacturer	Hornady
Produced	2020–present
Specifications
Parent case	.220 Russian/6.5mm Grendel[1]
Case type	Rimless, bottleneck
Bullet diameter	6.18 mm (0.243 in)[2]
Neck diameter	6.96 mm (0.274 in)[2]
Shoulder diameter	10.924 mm (0.4301 in)[2]
Base diameter	11.201 mm (0.4410 in)[2]
Rim diameter	11.20 mm (0.441 in)[3]
Rim thickness	1.5 mm (0.059 in)[1]
Case length	37.85 mm (1.490 in)[2]
Overall length	57.40 mm (2.260 in)[2]
Case capacity	2.20 cm3 (34.0 gr H2O)[citation needed]
Rifling twist	190.5 mm (1:7.50 in)
Primer type	Small rifle
Maximum pressure (SAAMI)	358.53 MPa (52,000 psi)[2]
Ballistic performance
Bullet mass/type Velocity Energy 6.67 g (103 gr) ELD-X Precision Hunter 853.44 m/s (2,800.0 ft/s) 2,429 J (1,792 ft⋅lbf) 6.80 g (105 gr) BTHP BLACK 838.2 m/s (2,750 ft/s) 2,388 J (1,761 ft⋅lbf) 7.00 g (108 gr) ELD Match 838.2 m/s (2,750 ft/s) 2,459 J (1,814 ft⋅lbf)
Test barrel length: 610 mm (24 in) Source(s): [4]

The 6mm Advanced Rifle Cartridge (6×38mm), or 6mm ARC for short, is a 6 mm (.243) caliber intermediate rifle cartridge introduced by Hornady in 2020, as a low-recoil, high-accuracy 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.^[4]

The cartridge makes use of 6 mm (.243 in) bullets, which are known for their high ballistic coefficients due to the high sectional density with less drag and better energy retention at extended ranges. With the release in 2020, Hornady also launched three factory loads with 103, 105 and 108 gr (6.7, 6.8 and 7.0 g) bullet weights and advertised G1 ballistic coefficients of .512, .530 and .536 respectively.^[5]

The 6mm ARC is a medium-power cartridge comparable to the 6.5mm Grendel, 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 6mm Creedmoor, but out of a compact cartridge that 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.

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,^[6] for example, has two sets of data. The first set of data is loaded to the SAAMI maximum average pressure (MAP) of 52,000 psi, 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, which is stated to be for use with bolt action guns such as the CZ 527. The Hornady manual states that this second set of data should not be used in gas-guns. Due to the lower MAP, the performance of 6mm ARC ammunition loaded to 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.

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For an ordinary AR-15 rifle chambered for the .223 Rem/5.56mm NATO, a new barrel, magazine and bolt are required to convert to the 6mm ARC.^[7] The 6mm ARC utilizes the same bolt head size as the 6.5mm Grendel, and 6.5mm Grendel-compatible AR-pattern box magazines have also been used successfully with the 6mm ARC.^[8] The 6mm ARC therefore can also be a suitable chambering for shorter "mini-action" bolt-action rifles, such as the CZ 527 bolt action rifle mentioned previously.

• .223 Remington
• 6mm AR
• 6 PPC
• 6.5mm Grendel