|6 mm Advanced Rifle Cartridge|
|Place of origin||United States|
|Parent case||5.6×39 mm (.220 Russian), 6.5mm Grendel|
|Case type||Rimless, bottleneck|
|Bullet diameter||6.18 mm (0.243 in)|
|Neck diameter||6.96 mm (0.274 in)|
|Shoulder diameter||10.924 mm (0.4301 in)|
|Base diameter||11.201 mm (0.4410 in)|
|Rim diameter||10.44mm* (0.4410 in)|
|Rim thickness||1.5 mm (0.059 in)|
|Case length||37.85 mm (1.490 in)|
|Overall length||57.40 mm (2.260 in)|
|Case capacity||2.20 cm3 (34.0 gr H2O)|
|Rifling twist||190.5 mm (1:7.50")|
|Primer type||Small rifle|
|Maximum pressure (SAAMI)||358.53 MPa (52,000 psi)|
|Test barrel length: 610 mm (24 in)|
The 6 mm Advanced Rifle Cartridge (6×38mm), or 6mm ARC for short, is a 6mm (.243) caliber intermediate rifle cartridge introduced by Hornady in 2020, as a low-recoil, high-accuracy long-range cartridge designed for the AR-15 platform.
The cartridge makes use of 6 mm (.243) 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.
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. 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. The 6mm ARC therefore can also be a suitable chambering for shorter "mini-action" bolt-action rifles.