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.400 Legend AR-15 Complete Uppers

Build a powerful and reliable straight-wall hunting rifle with a 400 Legend AR-15 upper receiver assembly from Mid State Firearms. Designed for hunters who want more performance than the .350 Legend while avoiding the heavier recoil of larger cartridges, the .400 Legend delivers excellent energy, accuracy, and versatility in a compact AR-15 platform.

Our complete .400 Legend uppers are built for dependable field performance and are ready to install on your existing AR-15 lower receiver. Whether you’re preparing for deer season, hunting in a straight-wall cartridge state, or building a dedicated big-game AR, a properly assembled upper is the foundation of a reliable rifle.

Why Choose a .400 Legend AR-15 Upper?

The .400 Legend was designed specifically for hunters who want increased terminal performance while maintaining the familiar handling and customization of the AR-15 platform. With a larger diameter bullet and excellent downrange energy, it provides a capable option for whitetail deer, hogs, and other medium-sized game.

Benefits of the .400 Legend cartridge include:

* Greater bullet diameter and energy than the .350 Legend
* Less recoil than larger straight-wall AR cartridges
* Excellent performance for deer hunting and other medium game
* AR-15 compatibility with a 6.8 SPC
* Straight-wall cartridge compliance in many hunting areas

## Built, Inspected, and Ready to Hunt

At Mid State Firearms, our AR-15 uppers are properly assembled with attention to fit, function, and reliability. Every upper is inspected before shipping to ensure components are installed correctly and ready for use.

When a .400 Legend upper is ordered with a bolt carrier group, we test fire the upper using that exact BCG to verify reliable cycling and proper function. This gives 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 checked for real-world performance before it leaves our facility.

## Complete Your .400 Legend Build

A complete .400 Legend AR-15 upper requires a compatible lower receiver, magazines, and a **6.8 SPC  bolt**. Pair your upper with a quality lower receiver and ammunition designed for the .400 Legend cartridge for a dependable hunting setup.

Browse our selection of .400 Legend AR-15 uppers and build a straight-wall hunting rifle designed for accuracy, reliability, and performance in the field.