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CMMG Mk3 6 5 Creedmoor 308 WIN 8 6 BLK High Pressure Bolt Carrier Group Black Phosphate 65BA4D6 UPC 815835018997
Product Description
The CMMG® Mk3 High Pressure Bolt Carrier Group (SKU: 65BA4D6 / UPC: 815835018997) is engineered specifically to eliminate cycling failures and primer extrusion issues common in large-frame semi-automatic precision rifles. Purpose-built for the high-pressure dynamics of the 6.5 Creedmoor, hot .308 Winchester handloads, and high-energy 8.6 Blackout loadings, this complete drop-in BCG brings match-grade reliability and extended operational endurance to your DPMS-pattern LR-308 or SR-25 platform build.
Built without compromise from superior metallurgical stock, the bolt carrier is precision-machined from case-hardened AISI 8620 steel and features a hard-chrome-lined internal bore and gas key to resist high-velocity hot gas erosion and ease carbon cleanup. The high-pressure bolt is machined from premium Carpenter 9310 alloy steel—shot-peened and magnetic particle inspected (MPI) to identify microscopic surface fractures—while the heavy-duty extractor is crafted from impact-resistant S7 tool steel. The entire exterior is treated with a rugged MIL-DTL-16232 Manganese Phosphate finish that holds lubricating films far longer than bare steel while shielding critical working surfaces from moisture, chemical solvents, and abrasive field grit.
What sets the CMMG 65BA4D6 apart is its dedicated high-pressure firing pin system. Standard .308 firing pins feature larger tip diameters and wide bolt face apertures that allow softened primers on high-pressure cartridges to flow backward into the firing pin channel, causing blown primers, cratering, and firing pin shear. CMMG solves this by mating a hardened 17-4 PH stainless steel firing pin featuring a reduced 0.060-inch tip with a matched narrow-aperture bolt face. Combined with a properly torqued and staked gas key secured by Grade 8 fasteners, this assembly delivers reliable extraction, flawless feeding, and long-term headspace stability under sustained strings of fire.
*Armorer Bench Notes & Real-World Staging Guidance:*
Fitment Matrix: Direct fit for CMMG Mk3, Aero Precision M5, DPMS LR-308 Gen 1, PSA PA-10, and standard SR-25 pattern large-frame upper receivers chambered in 6.5 Creedmoor, .308 Win, 7.62x51mm NATO, 8.6 BLK, and .260 Rem. CRITICAL: This BCG is built to DPMS LR-308 dimensions and is NOT compatible with Armalite AR-10B pattern rifles, DPMS GII small-frame uppers, or standard AR-15 (5.56 NATO) platforms. Due to varying barrel extension tolerances among large-frame manufacturers, always verify chamber headspace with certified SAAMI GO and NO-GO gauges before live-fire staging. Generously lubricate the four contact rails, cam pin slot, and gas ring body with high-temp synthetic weapon oil prior to installation.
- Ensure the host firearm is completely clear, magazine removed, and chamber visually and physically verified empty.
- Unbox the bolt carrier group and wipe away all factory preservative oils; inspect the gas key staking and confirm free travel of the 17-4 PH firing pin.
- Apply generous drops of synthetic gun oil to the four external carrier guide rails, the cam pin track, and the exterior of the bolt behind the gas rings.
- Pull the bolt forward into its unlocked operational orientation and slide the complete BCG assembly into the upper receiver along the charging handle channel.
- Conduct dry-fire cycling and function checks: verify smooth lockup into the barrel extension, positive lock-back on an empty magazine follower, and clean ejection of dummy training rounds.
Key Features
- High-Pressure Bolt & Firing Pin Architecture: Employs a reduced 0.060-inch 17-4 PH stainless steel firing pin and narrowed bolt face channel to eliminate primer cratering, pierced primers, and flow under high-pressure 6.5 Creedmoor and .308 loads.
- 9310 Steel Bolt Assembly: CNC-machined from ultra-high-strength Carpenter 9310 alloy steel, shot-peened, and magnetic particle inspected (MPI) to guarantee maximum lug sheer strength.
- Hardened S7 Tool Steel Extractor: Features high shock-resistance S7 tool steel construction paired with an enhanced spring and buffer assembly for positive rim engagement and reliable high-speed brass ejection.
- Hard Chrome Lined Internal Bore: Carrier interior bore and gas key channel are chrome-lined to provide a gas-tight seal, resist corrosive combustion gases, and streamline cleaning.
- TDP-Spec Staked Gas Key: 4140 steel gas key attached with Grade 8 fasteners, torqued to specification, and aggressively staked to eliminate loosening under aggressive gas cycling.
- Manganese Phosphate Protective Coating: Heavy-duty matte black phosphate finish absorbs and retains weapon lubricants while providing extreme abrasion and corrosion resistance.
Product Specifications
- Brand: CMMG®
- Model/Series: Mk3 High Pressure Bolt Carrier Group
- MPN / SKU: 65BA4D6 / CMMG-65BA4D6
- UPC: 815835018997
- Platform Compatibility: DPMS LR-308 / CMMG Mk3 / SR-25 Pattern Large-Frame AR Receivers
- Caliber Chambering: 6.5 Creedmoor, .308 Winchester, 7.62x51mm NATO, 8.6 BLK, 6mm Creedmoor, .260 Rem
- Carrier Material: AISI 8620 Alloy Steel (Chrome Lined Bore & Key)
- Bolt Material: Carpenter 9310 Alloy Steel (MPI & Shot-Peened)
- Extractor Material: S7 Tool Steel
- Firing Pin Material: 17-4 PH Stainless Steel (0.060 in High-Pressure Tip)
- Gas Key Fasteners: Grade 8 Screws, Staked per TDP
- Surface Finish: MIL-DTL-16232 Manganese Phosphate
- Country of Origin: United States of America
