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. Related