M4E1 .300 Bo Assembl Uppr Rcvr M4 10'' Bbl Pistol-Length Blk

The Aero Precision M4E1 .300 Blackout assembled upper receiver is a straightforward, quality-built upper for shooters and builders who want to dial in their own bolt carrier group and charging handle. Chambered in .300 Blackout and built around a 10-inch chrome moly barrel with a pistol-length gas system, this upper comes ready to integrate into your AR-15 platform—you just need to supply your own BCG and charging handle. The 9-inch handguard gives you solid real estate for grip and accessory mounting without weighing down a compact build, and the low-profile gas block keeps the profile clean. Black anodizing and USA manufacturing mean you're getting a platform built to last through range sessions, hunting trips, or whatever you're building toward.

This is an assembled upper, not a complete one, which actually works in your favor: you're not paying for components you might want to swap anyway. The .300 Blackout cartridge shines in short-barrel applications like this—delivering serious velocity and energy downrange while staying subsonic when loaded appropriately. Whether you're building a truck gun, a home-defense AR, or an integrally suppressed setup, starting with a solid upper like this gives you a foundation you can trust.

A few things to know: the standard A2 flash hider is included but is not pinned or welded to the barrel. If you're planning a rifle build (16 inches or longer overall length), you'll need to pin and weld the muzzle device per ATF regulations to hit that legal rifle length. As delivered, this upper is a blank canvas—bring your own BCG, charging handle, and lower to complete the build.

Key Features

• .300 Blackout chambering optimized for shorter barrels
• 10-inch chrome moly barrel with carbine-length gas system
• Low-profile gas block for a cleaner silhouette
• 9-inch M-LOK handguard for accessory mounting and forward grip space
• Standard A2 flash hider included (not pinned/welded)
• Black anodized finish
• Made in the USA
• Bolt carrier group and charging handle not included—personalize your build

Specifications

Frequently Asked Questions

What comes in the box and what do I need to add?

This is an assembled upper receiver—you get the barrel, handguard, gas system, and muzzle device. You'll need to source a bolt carrier group, charging handle, and lower receiver to complete a functional rifle.

Is the muzzle device pinned and welded?

No. The A2 flash hider is removable as shipped. If you're building a rifle (16 inches or longer), you'll need to pin and weld the muzzle device yourself or have a gunsmith do it to meet ATF length requirements.

What's the advantage of .300 Blackout in a 10-inch barrel?

The .300 Blackout cartridge was designed for short barrels and delivers excellent velocity and energy even at lengths like 10 inches where many other rounds lose efficiency. It's also subsonic-capable with appropriate ammunition.

Will this upper fit on my existing lower receiver?

Yes, as long as your lower is a standard AR-15 platform receiver. This is a direct-fit assembled upper for any mil-spec or commercial-spec AR-15 lower.