CMMG Resolute Mk4 .300 Blackout 16.1" Upper Group - Armor Black - 30BC40AAB
Product Description
Top off your next custom AR build or expand your caliber rotation with the premium **CMMG® Resolute® Mk4 Upper Group**. This factory-assembled barreled receiver is purpose-built for the hard-hitting .300 AAC Blackout cartridge, bridging the gap between close-quarters performance and intermediate-range ballistic superiority. Because it comes **assembled without a bolt carrier group (BCG) or charging handle**, it gives builders complete freedom to integrate their preferred custom components. It drops natively onto any standard AR-15 lower receiver assembly, transforming a standard baseline configuration into a heavy-hitting weapon system.
The upper receiver is precision-machined from robust **billet 6061-T6 aluminum**, ensuring tight structural tolerances and superior stiffness compared to common cast components. Protecting the aluminum unibody and handguard is a uniform coat of premium **Cerakote finish in Armor Black**. This high-grade layer shields the underlying alloy from corrosive carbon slurry, environmental trail sweat, and abrasive holster wear. At its core is a 16.10-inch 4140 Chrome-Moly steel barrel treated with a Salt Bath Nitride (SBN) finish inside and out for exceptional bore longevity and rust resistance. Custom rifled with a **1:7 twist rate**, the barrel stabilizes a vast spectrum of projectiles—from fast supersonic hunting loads to heavy subsonic duty rounds.
In terms of accessory integration, this optics-ready upper group features the modernized **CMMG EML™ 15 handguard**. This slim, free-floating handguard features functional M-LOK® attachment slots situated at the 3, 6, 9, and 12 o'clock positions. By removing the full-length top Picatinny rail section found on legacy systems, CMMG significantly slashes front-end weight while leaving a dedicated upper segment for front backup iron sights or active laser modules. Driven by a dependable direct-impingement carbine-length gas track paired with an **adjustable 0.750" gas block**, tuning the system to transition smoothly between suppressed and unsuppressed shooting cycles is precise and straightforward.
*Armorer Bench Notes & Technical Assembly Guidance: The 30BC40AAB upper assembly arrives pre-fit with a standard CMMG A2 flash hider over 5/8x24 muzzle threads, which can easily be removed to install a dedicated silencer muzzle brake or direct-thread suppressors. Because this configuration does not include a BCG or charging handle, you must ensure your sourced parts meet matching tolerances: pair it with a high-quality full-auto profile M16 bolt carrier group headspace-verified for 5.56 NATO/.300 BLK. When mounting optics on your continuous billet top rail, push mount blocks forward against the Picatinny lug walls before torquing to specification. Clean carbon scale away from the gas block adjustment port during your routine bench maintenance to prevent unburnt powder debris from locking the regulator screw over long shooting strings.
Key Features
- Builder-Ready Barreled Assembly: Ships fully assembled minus the BCG and charging handle, giving you the flexibility to complete the upper with your preferred components.
- Premium Armor Black Cerakote: Coated in a professional-grade Armor Black Cerakote finish that shields the metal from impact scratches, weather elements, and harsh solvents.
- 16.10-Inch Nitrided Steel Barrel: Crafted from 4140 Chrome-Moly steel with a Salt Bath Nitride finish and 1:7 twist, ensuring durable downrange accuracy with all bullet weights.
- Modern CMMG EML 15 Handguard: Features an ultra-lightweight free-float design with 4-sided M-LOK mounting slots to securely host tactical lights, vertical grips, and rail scales.
- Adjustable 0.750" Gas Block: Outfitted with an adjustable gas system that allows operators to easily dial in gas restriction levels for uncompromised suppressed reliability.
Product Specifications
- Brand: CMMG
- Model Line: Resolute® Mk4 Upper Receiver Group
- MPN/SKU: 30BC40AAB (Also tracked as 30BC40A-AB)
- UPC Code Profile: 810103473393
- Caliber Focus: .300 AAC Blackout (300 BLK / 7.62x35mm)
- Barrel Length: 16.10 Inches
- Barrel Material: 4140 Chrome-Moly Steel with Salt Bath Nitride (SBN) Finish
- Barrel Twist Rate: 1:7 Twist Configuration
- Operating System Type: Direct Impingement (Carbine-Length Gas Track)
- Gas Block Specification: Adjustable 0.750" Gas Block
- Upper Receiver Style: Precision-Machined Billet 6061-T6 Aluminum
- Handguard System: CMMG EML 15" Free-Float M-LOK Rail
- Exterior Coating Finish: Elite Armor Black Cerakote Finish
- Muzzle Device Interface: Standard CMMG A2 Flash Hider (5/8x24 Thread Taper)
- Bolt Carrier Group: Not Included
- Charging Handle: Not Included
- Overall Upper Length: 25.0 Inches
- Net System Mass: 3.4 lbs (Featherweight Unloaded Substructure)
- Country of Manufacture: United States
