6 mm ARC (Advanced Rifle Cartridge) delivers 108- to 115-grain bullets at supersonic speeds past 1,000 yards while fitting a standard-length AR-15 action. Arm or Ally stocks 16″, 18″, and 20″ 416R stainless barrels in 1:7.5 twist—the sweet spot for long, high-BC 6 mm projectiles. Each barrel carries a DPMS-style extension, optimized feed ramps, and a rifle or intermediate gas system to reduce bolt velocity and extend case life. Tuneable gas blocks and LMT-pattern enhanced BCGs are available to complete a soft-shooting, match-grade package. Whether you compete in precision carbine matches or need a lightweight predator rifle with flat-shooting reach, our 6 mm ARC barrels unlock ballistic performance previously reserved for large-frame rifles.