16″ .400 Legend AR-15 Upper Receiver – 4150 CMV Nitride Barrel
Build a powerful and reliable straight-wall hunting AR-15 with the Mid State Firearms 16″ .400 Legend Complete Upper Receiver. Designed for hunters and shooters looking for increased performance without stepping up to the recoil of larger cartridges, the .400 Legend delivers excellent energy, accuracy, and versatility in the familiar AR-15 platform.
This upper features a 16-inch 4150 CMV .400 Legend barrel with a durable nitride finish, carbine-length gas system, and 1:16 twist rate optimized for stabilizing common .400 Legend hunting loads. The barrel is threaded 5/8×24 for compatibility with a wide variety of muzzle devices and suppressors.
The upper receiver is built around a 7075-T6 aluminum mil-spec upper receiver with an enlarged big bore ejection port designed specifically for larger AR cartridges. It includes a forward assist and dust cover for a traditional, fully equipped AR configuration.
Built for Reliable .400 Legend Performance
Every Mid State Firearms upper is properly assembled and inspected before shipping. We focus on reliable function, correct installation, and quality components so your upper is ready for your next build.
When you add a bolt carrier group and charging handle through the available options, we test fire the upper using that exact BCG before it ships. This confirms proper cycling and function with your selected components, giving you confidence that your upper is ready to pin onto your AR-15 lower receiver and go.
No guesswork. No troubleshooting. Just a properly assembled upper that has been function tested before it leaves our facility.
Features
- Caliber: .400 Legend
- Barrel Length: 16″
- Barrel Material: 4150 CMV
- Barrel Finish: Nitride
- Twist Rate: 1:16
- Gas System: Carbine Length
- Gas Block Journal: .750″
- Muzzle Thread: 5/8×24
- Muzzle Device: A2 Flash Hider
- Handguard: 15″ 7-Sided M-LOK Free Float Handguard
- Upper Receiver: 7075-T6 Aluminum Mil-Spec Upper
- Upper Finish: Type III Hardcoat Anodized Black
- Ejection Port: Enlarged Big Bore Ejection Port
- Gas Block: .750 Low Profile Gas Block
- Gas Tube: Carbine Length Gas Tube
- Forward Assist: Included
- Dust Cover: Included
.400 Legend AR-15 Compatibility
The .400 Legend is a powerful straight-wall cartridge designed for hunters who want increased bullet diameter and terminal performance while maintaining the modularity and ergonomics of the AR-15 platform.
A .400 Legend build requires:
- A compatible 6.8 SPC pattern bolt
- Compatible magazines
- Quality factory .400 Legend ammunition
This upper is designed to install onto a standard AR-15 lower receiver with the appropriate .400 Legend components.
Complete Your Build by adding these:
Choose your preferred configuration with optional upgrades for:
- Bolt Carrier Group
- Charging Handle
When these options are selected, Mid State Firearms test fires your upper with the exact BCG included in your order to verify reliable operation before shipping.
Whether you’re building a dedicated deer rifle, straight-wall hunting AR, or a powerful all-purpose upper, this .400 Legend AR-15 upper receiver provides the performance, reliability, and confidence you need in the field.
sound of freedom – This was a great set up. I loved being able to customize the set up. Only issue I had was my own fault as a newb to building these. I used a heavy barrel in a slim hand guard. It makes adding attachments tough with clearances. Hoping someday to also get an AR10 from here.