338 ARC Upper 10.5″ 1:5 Twist Upper with Options

CM15 338 ARC 10.5″ Upper

• CM 6061 lightweight billet aluminum receiver
  • Reliefs featured throughout the receiver
  • Picatinny rail milled channel for a sleek/light weight option
• CM 6061 9.5″ MLOK handguard
  • QD Sockets at 3 and 9 o’clock
  • Full Picatinny top rail
• Choice of Suppressor Host Muzzle Device or Thread Protector
• CM15 Low Mass Bolt Carrier Group
  • 9310 Hardened Steel Bolt
  • 17-4 Stainless Steel Firing Pin
  • 8620 Carrier and Key
  • MPI Tested
  • Hardened Extractor S7 Steel
• CM15 Warhammer Ambidextrous Charging Handle – in collaboration with Breek Arms
• Superlative Arms Adjustable Gas Block
• CM Melonite Gas Tube
• CM15 338 ARC 10.5″ Barrel
  • 416R Stainless Steel
  • Medium Profile
  • QPQ Corrosion Resistant
  • 1:5 Twist
  • Pistol Gas
  • .750 Gas Journal
  • 5/8×24 threaded muzzle

CM15 10.5″ 338 ARC Upper: The Ultimate Subsonic Sledgehammer

Step into the next evolution of big-bore performance with the CM15 338 ARC 10.5″ Upper. Purpose-built for the revolutionary 338 Advanced Rifle Cartridge, this upper receiver group is designed for shooters who want to bridge the gap between standard AR-15 maneuverability and the devastating terminal ballistics of .338 caliber projectiles.

Unmatched Stabilization with 1:5 Twist

The 338 ARC shines when pushing heavy, high-BC bullets, particularly in subsonic applications. To handle these massive projectiles, our 10.5-inch barrel features an ultra-fast 1:5 twist rate. This aggressive rifling ensures that heavy-grain bullets are perfectly stabilized the moment they leave the muzzle, providing surgical precision and preventing keyholing—even when running a suppressor.

Compact, Reliable, and Versatile

The 10.5″ barrel length offers the perfect “short-barrel rifle” (SBR) or pistol profile, making it an ideal choice for brush hunting, vehicle operations, or home defense. Built on a foundation of 7075-T6 aluminum, the upper features an enlarged ejection port to ensure the wider .338 brass cycles with flawless reliability.

Product Features:

• Caliber: 338 ARC (Optimized for heavy .338 projectiles).

• 10.5” Heavy Barrel: 4150 CMV steel with a 1:5 twist for maximum stability.

• Tailored Options: Customize your build with selectable M-LOK handguards, high-performance BCGs, and specialized muzzle devices.

• AR-15 Compatible: Fits standard lowers; utilizes 6.5 Grendel-style magazines.

Whether you are building a dedicated suppressed “thumper” or a compact hunter, the CM15 338 ARC 10.5″ Upper delivers heavy-hitting authority in a lightweight, modern package.