CMMG AR15 12.5" 300BLK Mr Barrel
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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.
Specifications
Build history on GunPartPicker
Builders have been adding the CMMG AR15 12.5" 300BLK Mr Barrel to their builds on GunPartPicker since February 2026. All time, it ranks #240 of the 814 barrels builders have added.
Availability is good: it was in stock at one retailer or another nearly every day in August 2026, and today 3 of the 6 retailers we track have it in stock. It dipped to $149.67 at Brownells for a stretch in August 2026, well under its usual $181.99, so sales do come around. Buying today, the lowest price is $193.99 at Palmetto State Armory, above August's low of $149.67, so a better deal may come back.
Updated · from real builds on GunPartPicker · Prices checked · refreshed daily across 35 retailers
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Frequently Built With
The part most often added in each category by the 5 builds that include this one
Tacfire AR-15 Upper Receiver with Dust Cover and Forward Assist - UP01-C
Wilson Combat Wc-15 Billet Lower Receiver
CMMG AR15 Ambi Mag Catch, Black - 55AFF6E
Phase 5 Tactical AR-15 90 Degree Ambi Safety Selector Black
Strike Industries T-Bone AR-15 Charging Handle for .223/5.56 - Black/Black
Strike Industries Viper 25 deg Enhanced Pistol Grip for AR-15 and AR-10 Receiver Style Rifles, Black - ARVEPG25
Build Configuration Breakdown
Aggregated and anonymized data showing how builders use this product
PlatformBased on real build data showing which platform (AR-15, AR-10, AR-9) builders pair with this product.
Builds Featuring This Part
See all 2 →Builds in the community that include the Cmmg Ar15 12.5" 300blk Mr Barrel
| Build | Parts | Total |
|---|---|---|
 | 15 | $1128.57 |
 | 21 | $1277.91 |
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