
Availability: In Stock
Current Stock: Out of stock
The CMMG 57D400F is a 16.1" barrel sub-assembly designed for shooters building or upgrading an AR-platform rifle in 5.7x28mm. This is a complete barrel assembly—not just a tube—which means you get a ready-to-install component that simplifies the build process for gunsmiths, competition shooters, and DIY builders who want to swap calibers or experiment with the 5.7x28mm cartridge without sourcing individual parts. The 4140CM steel construction delivers the durability and precision you'd expect from CMMG's manufacturing, a brand known for quality in the AR platform ecosystem.
The 5.7x28mm is a niche cartridge that appeals to shooters interested in reduced recoil, lower noise levels, and diminished shooter fatigue—qualities that make it valuable for training, close-range tactical work, or dedicated range sessions. A 16.1" barrel strikes a practical balance between velocity, handling, and overall rifle length, suitable for both bench and field use without the complexity of shorter configurations. Because this is a sub-assembly, installation is faster than assembling a barrel from loose components, and you benefit from CMMG's engineering rather than piecing together parts from different makers.
This barrel assembly is built for shooters who already understand AR-platform mechanics and are ready to dive into 5.7x28mm shooting. Whether you're a precision rifle enthusiast exploring a new cartridge, a competitive shooter testing reduced-recoil loads, or someone curious about 5.7x28mm ballistics, the CMMG 57D400F offers a straightforward, pre-engineered solution to get you on target.
| Brand | CMMG |
| Model | 57D400F |
| Caliber | 5.7x28mm |
| Barrel Length | 16.1" |
| Material | 4140CM Steel |
| Type | Barrel Sub-Assembly |
A barrel sub-assembly is a complete, pre-assembled component ready for installation into an AR platform. Unlike a standalone barrel tube, it includes integrated parts and engineering optimized by the manufacturer for straightforward installation, reducing the need to source and assemble individual components yourself.
This is a 5.7x28mm assembly designed for AR platforms configured for that caliber. Compatibility depends on your upper receiver and bolt carrier group being rated for 5.7x28mm. Verify your rifle's specs before installation.
5.7x28mm is a modern rifle cartridge known for reduced recoil, lower noise signature, and diminished shooter fatigue compared to many rifle calibers. It's popular for training, precision range work, and shooters seeking a softer shooting experience.
You receive the barrel sub-assembly itself. Installation into a compatible AR upper requires your existing upper receiver and bolt carrier group rated for 5.7x28mm.

SKU: 126514116 • Width: 1.9in • Height: 1.8in • Depth: 17.6in • Weight: 2.02oz





Availability: In Stock
Current Stock: Out of stock
The CMMG 57D400F is a 16.1" barrel sub-assembly designed for shooters building or upgrading an AR-platform rifle in 5.7x28mm. This is a complete barrel assembly—not just a tube—which means you get a ready-to-install component that simplifies the build process for gunsmiths, competition shooters, and DIY builders who want to swap calibers or experiment with the 5.7x28mm cartridge without sourcing individual parts. The 4140CM steel construction delivers the durability and precision you'd expect from CMMG's manufacturing, a brand known for quality in the AR platform ecosystem.
The 5.7x28mm is a niche cartridge that appeals to shooters interested in reduced recoil, lower noise levels, and diminished shooter fatigue—qualities that make it valuable for training, close-range tactical work, or dedicated range sessions. A 16.1" barrel strikes a practical balance between velocity, handling, and overall rifle length, suitable for both bench and field use without the complexity of shorter configurations. Because this is a sub-assembly, installation is faster than assembling a barrel from loose components, and you benefit from CMMG's engineering rather than piecing together parts from different makers.
This barrel assembly is built for shooters who already understand AR-platform mechanics and are ready to dive into 5.7x28mm shooting. Whether you're a precision rifle enthusiast exploring a new cartridge, a competitive shooter testing reduced-recoil loads, or someone curious about 5.7x28mm ballistics, the CMMG 57D400F offers a straightforward, pre-engineered solution to get you on target.
| Brand | CMMG |
| Model | 57D400F |
| Caliber | 5.7x28mm |
| Barrel Length | 16.1" |
| Material | 4140CM Steel |
| Type | Barrel Sub-Assembly |
A barrel sub-assembly is a complete, pre-assembled component ready for installation into an AR platform. Unlike a standalone barrel tube, it includes integrated parts and engineering optimized by the manufacturer for straightforward installation, reducing the need to source and assemble individual components yourself.
This is a 5.7x28mm assembly designed for AR platforms configured for that caliber. Compatibility depends on your upper receiver and bolt carrier group being rated for 5.7x28mm. Verify your rifle's specs before installation.
5.7x28mm is a modern rifle cartridge known for reduced recoil, lower noise signature, and diminished shooter fatigue compared to many rifle calibers. It's popular for training, precision range work, and shooters seeking a softer shooting experience.
You receive the barrel sub-assembly itself. Installation into a compatible AR upper requires your existing upper receiver and bolt carrier group rated for 5.7x28mm.
SKU: 126514116 • Width: 1.9in • Height: 1.8in • Depth: 17.6in • Weight: 2.02oz
