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Swapping calibers or building out a dedicated 6.5 Grendel or 6mm ARC upper means you need a bolt carrier group cut for the job, and this one from CMMG is a drop-in answer. It ships as a complete assembly, so there's no sourcing separate bolts, extractors, or gas keys. It runs in standard AR variants and covers both 6.5 Grendel and the newer 6mm ARC, since the two cartridges share the same case head and bolt face. Just note it isn't compatible with CMMG's MkW platform.
The materials here are what you'd want to see on a hard-use BCG. The bolt is machined from 9310 steel, a modern alloy known for its toughness and fatigue resistance, which matters most at the lugs where bolts tend to take a beating. The carrier is 8620 steel, chrome lined for smooth cycling and long life, and the extractor is 4140 steel. Every part wears a phosphate finish that holds oil well and shrugs off corrosion, which is exactly what you want on a rifle that sees range time, field use, or weather.
There's a reason CMMG mixes these alloys instead of using one steel throughout. The 8620 carrier is the longtime standard for AR carriers because its case-hardened surface handles the constant back-and-forth motion while the softer core absorbs impact without cracking. The 9310 bolt brings extra strength where the stress concentrates, so it holds up under the higher pressures these cartridges generate. It's a proven pairing that balances durability and smooth function.
This is a straightforward install for anyone comfortable working on an AR. Drop it into a Mil-Spec upper with a matching 6.5 Grendel or 6mm ARC barrel, run a good lubricant, and you're set. It works as either a fresh build component or a replacement when your old bolt has racked up the rounds. CMMG backs every part they make with a Lifetime Quality Guarantee.
Yes, this bolt carrier group is built to run either cartridge. The 6mm ARC is based on the 6.5 Grendel case, so the two share the same case head and bolt face. Pair it with the matching barrel for whichever caliber you're running and you're good to go.
It's a complete assembly, not a bare bolt. That means you get the carrier, bolt, extractor, and gas key all put together and ready to drop in. No extra parts to source or assemble.
It's designed for standard AR variants and drops into a Mil-Spec upper with a 6.5 Grendel or 6mm ARC barrel. The one exception is CMMG's own MkW platform, which this BCG is not compatible with. If you're running a typical AR-15 setup, it'll fit right in.
9310 is a modern alloy steel valued for its toughness and fatigue resistance, which is exactly what you want at the bolt lugs where stress concentrates. It stands up well to the higher pressures these cartridges produce. Paired with the chrome-lined 8620 carrier, it's a combination built for reliable, long-term function.
| UPC | 810046230794 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | 64BA44F |
| Product Type | Bolt Carrier Group |
| Color | Black |
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