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CMMG
Overview
The CMMG AR-15 12.5" 300 Blackout MR Barrel is designed for optimized performance with a medium profile that balances weight and rigidity, making it ideal for various shooting applications. With a twist rate of 1:7, this barrel effectively stabilizes heavier projectiles, enhancing accuracy and terminal ballistics. The pistol-length gas system and .750 gas block diameter ensure reliable cycling, which is essential for builds tailored for short-barreled configurations or those seeking compact setups. This barrel is commonly integrated into builds that focus on the 300 Blackout caliber, particularly where a pistol gas system is preferred.
Based on build data

Wilson Combat Ar-15 Billet Upper Receiver
Upper Receiver
BLEM PSA AR15 Complete Classic Stealth Lower, Black
Lower Receiver
Battle Arms Development Rack Ambidextrous Ar-15 Charging Handle - Mod C
Charging Handle
Wilson Combat Ar-15 Lo-Profile Gas Block .750" Black
Gas Block
Wmd Guns Ar-15 Gas Tube Nitromet Mid-Length
Gas Tube
Aero Precision M4e1 Complete Lower Receiver W/moe Sl Grip & Sl-S Carbine Stock
Lower ReceiverAggregated and anonymized data showing how builders use this product
| Product | Category | Times Built Together |
|---|---|---|
| Wilson Combat Ar-15 Billet Upper Receiver | Upper Receiver | 153 |
| BLEM PSA AR15 Complete Classic Stealth Lower, Black | Lower Receiver | 146 |
| Battle Arms Development Rack Ambidextrous Ar-15 Charging Handle - Mod C | Charging Handle | 144 |
| Wilson Combat Ar-15 Lo-Profile Gas Block .750" Black | Gas Block | 136 |
| Wmd Guns Ar-15 Gas Tube Nitromet Mid-Length | Gas Tube | 132 |
| Aero Precision M4e1 Complete Lower Receiver W/moe Sl Grip & Sl-S Carbine Stock | Lower Receiver | 118 |
| Platform | Percentage |
|---|---|
| AR-15 | 88.2% |
| AR-10 | 9.1% |
| AR-9 | 2.6% |
| Caliber | Percentage |
|---|---|
| 300 Blackout | 100% |
| Gas System | Percentage |
|---|---|
| Pistol | 100% |
Builds in the community that include the Cmmg Ar15 12.5" 300blk Mr Barrel
| Build | Parts | Total |
|---|---|---|
![]() | 15 | $1091.76 |
![]() | 21 | $1252.87 |
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