Cmmg Ar15 12.5'' 300Blk Mr Barrel

The CMMG AR-15 12.5" 300 Blackout barrel is a drop-in conversion barrel that transforms your existing AR platform into a 300 AAC Blackout shooter without requiring any additional modifications to your lower receiver, bolt carrier group, or magazines. Whether you're building a short-barreled rifle for home defense, suppressed shooting, or a compact hunting rig, this 12.5" barrel gives you genuine 7.62×39 ballistics in a package that uses all your standard AR-15 infrastructure—no new bolt, no mag compatibility headaches.

Built with CMMG's proprietary Wasp nitriding treatment, the barrel resists wear and corrosion from heavy use and adverse conditions. The 1-7" rifling twist handles the full range of 300 Blackout ammunition, from lightweight 110-grain supersonic rounds to heavy 220-grain subsonic loads, making it genuinely flexible for different shooting scenarios. The 5/8"-24 muzzle threads accept standard AR-.308 suppressors, flash hiders, and muzzle brakes—a huge advantage if you're building a modular short-barreled rig.

The gas port on this 12.5" model is positioned specifically for pistol-length gas systems, which pairs well with a compact receiver extension and makes for a genuinely handy firearm. This is a true plug-and-play upgrade: remove your existing barrel, install this one, and you're shooting 300 Blackout. No stripped parts, no gunsmith work. If you're already deep in the AR ecosystem and want to add a subsonic-ready or short-range hunting barrel without buying a whole new rifle, this CMMG barrel delivers genuine versatility at the barrel level.

Key Features

• Direct replacement barrel for AR-15 platform—no bolt carrier or magazine modifications needed
• 1-7" rifling twist handles 110 to 220-grain 300 Blackout loads
• Wasp nitriding treatment for corrosion and wear resistance
• 5/8"-24 muzzle threads accept standard AR-.308 suppressors and muzzle devices
• Gas port optimized for pistol-length gas systems
• 12.5" length balances maneuverability with velocity retention

Specifications

Frequently Asked Questions

Will this barrel work with my existing AR-15 bolt and magazines?

Yes. The 300 Blackout cartridge was designed to use the standard AR-15 bolt carrier group and accept full-capacity magazines. No modifications to your lower receiver or upper components are required—it's a barrel swap.

What gas system does the 12.5" barrel use?

This 12.5" model is configured for pistol-length gas systems. The gas port position is optimized for that configuration.

Can I use both supersonic and subsonic ammunition in this barrel?

Yes. The 1-7" rifling twist stabilizes bullet weights from 110 to 220 grains, so it handles both supersonic and subsonic loads.

What muzzle devices are compatible?

The barrel features 5/8"-24 muzzle threads, which accept standard AR-.308 suppressors, flash hiders, and muzzle brakes.