CMMG 30BC40AMB Resolute MK4 300 Blackout 16.10", Midnight Bronze, M-LOK Free-Float Handguard for AR-Platform (No BCG or Charging Handle)

The CMMG 30BC40AMB Resolute MK4 300 Blackout 16.10" upper receiver is purpose-built for shooters seeking a short-range, subsonic-ready AR platform optimized for suppressed fire and close-quarters applications. Chambered in 300 Blackout—a cartridge engineered for subsonic performance with suppressors—this complete upper assembly serves tactical professionals, hunters, and precision shooters who demand effective ballistics without excessive noise signature. The Midnight Bronze finish provides both aesthetic distinction and corrosion resistance, making this upper receiver an ideal choice for those building custom AR platforms for specialized roles.

Built on CMMG's proven Resolute platform, this upper features a free-floating M-LOK handguard that isolates barrel harmonics for improved accuracy and reduces contact between barrel and furniture—critical for consistent shot placement. The 16.10-inch barrel length strikes a balance between velocity retention and maneuverability, delivering reliable subsonic and supersonic 300 Blackout performance. M-LOK accessory mounting allows shooters to attach lights, lasers, vertical grips, and other tactical components without rail limitations. Note that this assembly ships without bolt carrier group or charging handle, allowing experienced builders to source OEM or matched components aligned with their specific mission requirements.

This upper receiver pairs seamlessly with any standard AR-15 lower receiver, making it compatible with existing platforms and lower builds. Its 300 Blackout chambering excels in suppressed configurations, where subsonic ammunition performance shines, but also cycles standard supersonic loads for extended-range work. Weighing just 3.92 pounds, it maintains balance and ergonomics without excess mass. Builders selecting this upper should pair it with quality BCG components and a reliable charging handle to ensure consistent cycling and longevity. Perfect for those assembling dedicated short-range systems or modernizing existing AR platforms with proven subsonic-rated capability.