M4E1 .300 Bo Assembl Uppr Rcvr M4 16'' Bbl Pistol-Length Blk

The Aero Precision M4E1 .300 Blackout assembled upper receiver gives you a solid, US-made foundation for a short-barrel or pistol-configuration AR-15 build. This 16-inch upper is pre-assembled and comes ready to integrate with your lower receiver—though you'll need to source your own bolt carrier group and charging handle, which means you can spec those components to match your exact needs and budget. The 16-inch chrome moly barrel is paired with a pistol-length gas system and low-profile gas block, a practical setup that keeps the action responsive while managing recoil in a compact package.

Built with Aero's reputation for precision machining, the upper features a mil-spec compatible design and black anodized finish. The 15-inch M-LOK handguard gives you plenty of real estate for mounting lights, lasers, or other tactical accessories, and the modular rail system is built to last. The included A2 flash hider is not pinned or welded, so keep in mind that if you're configuring this as a rifle (16-inch overall length requirement), you'll need to have the muzzle device permanently affixed to meet federal law.

Whether you're building a truck gun, a short-range hunting upper, or a compact home-defense AR, the M4E1 in .300 Blackout handles both supersonic and subsonic ammunition. The pistol-length gas tube is a proven platform that keeps the bolt carrier group working smoothly across a wide range of loads—especially handy if you're running suppressors and subsonic rounds. This is a no-nonsense, American-made component that respects your intelligence as a builder.

Key Features

• 16-inch chrome moly barrel chambered in .300 Blackout
• Pistol-length gas system with low-profile gas block
• 15-inch M-LOK handguard for accessory mounting
• Black anodized finish
• Standard A2 flash hider (not pinned or welded)
• Pre-assembled and ready to marry to your lower receiver
• Made in the USA

Specifications

Frequently Asked Questions

Does this upper come with a bolt carrier group and charging handle?

No. This is an assembled upper receiver only—it does not include the bolt carrier group or charging handle. This gives you the freedom to select those components separately based on your budget and performance preferences.

Can I use this as a pistol upper or do I need a rifle lower?

The upper itself is compatible with both rifle and pistol lower receivers. However, the overall firearm configuration (pistol vs. rifle) depends on how you assemble it with your lower and what stock or brace you choose. Be sure to verify your local and federal regulations before completing your build.

Is the muzzle device pinned and welded?

No. The A2 flash hider is not pinned or welded. If you're building a rifle configuration and need to meet the 16-inch overall length requirement, you will need to have the muzzle device permanently affixed by a gunsmith.

What ammunition does the .300 Blackout barrel handle?

The .300 Blackout barrel is designed for both supersonic and subsonic ammunition, making it versatile for hunting, target shooting, and suppressed shooting applications.