6mm ARC

The 6 mm Advanced Rifle Cartridge (6×38mm), or 6mm ARC for short, is a 6mm (.243) caliber full-power 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 bullet weights and advertised G1 ballistic coefficients of .512, .530 and .536 respectively.
Compatibility with the AR-15.
For an ordinary AR-15 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 AR-magazines have also been used successfully with the 6mm ARC. The 6mm ARC can also be a suitable chambering for shorter "mini-action" bolt action rifles.
Several firearm manufacturers have announced that they will be offering factory rifles chambered in the 6mm ARC.
Comparison with other cartridges.
Compared to .223 Remington.
Compared to .223 Remington/5.56×45mm NATO, the 6mm ARC has more recoil and heavier ammunition, but better long-range performance with less ballistic drop and wind drift, and more retained energy downrange.
Compared to .308 Winchester.
Compared to .308 Winchester/7.62×51mm NATO, the 6mm ARC has less recoil, better long-range performance in most cases in the form of less wind drift, better penetration in most cases and lighter ammunition. While the 6mm ARC has less muzzle energy, it can in some cases retain more of its energy downrange due to better ballistic coefficients.
Compared to other 6mm cartridges.
The 6mm ARC is a factory cartridge which has many similarities with the 6mm AR wildcat cartridge. The case volume of the 6mm ARC is about 2.20 mL (34 grains of water), and the volume therefore lies between those of the two popular 6 mm benchrest cartridges 6mm PPC of 2.10 ml (32 grains of water) and 6mm BR of 2.50 ml (38.5 grains of water). However, the 6mm AR and 6mm ARC separate themselves from the mentioned benchrest cartridges in that they were designed with a 30-degree shoulder angle to ensure reliable feeding in an AR-15 rifle.
Larger-sized AR-10 performance cartridges such as 6XC, 6×47mm Lapua, 6.5×47mm Lapua, 6mm Creedmoor and 6.5mm Creedmoor have better long range performance compared to the 6mm ARC, but have more recoil, as well as overall lengths that make them unable to fit in an AR-15 sized magazine well.