M4E1 300Blk Assembled Upper 10''Bbl Threaded W/Rm9.3'' Hg Fde

The Aero Precision M4E1 300 Blackout assembled upper with 10-inch barrel and threaded muzzle is a complete, ready-to-run upper receiver built for shooters who want a compact, capable platform for subsonic shooting, close-quarters hunting, or specialized tactical work. This upper comes fully assembled—just pair it with a lower receiver, bolt carrier group, and charging handle to complete your build. The 10-inch barrel length hits the sweet spot for 300 Blackout: short enough for maneuverability and hearing protection when running subsonic ammo, long enough to deliver reliable performance in a modern sporting rifle.

At the heart of this upper is Aero Precision's ATLAS R-ONE handguard, engineered to balance weight savings with mounting versatility. The R-ONE uses Aero's proprietary ATLAS attachment system—a proven platform that's slim and lightweight while maintaining the rigidity and strength Aero shooters expect. The full-length top picatinny rail accepts optics, backup sights, and accessories; quick-disconnect sling mounts at 3, 6, and 9 o'clock positions let you configure the rifle your way. The handguard is cut for low-profile gas blocks, and its dimensions (1.3" ID, 1.5" OD) keep the overall package compact without sacrificing real estate for lights, lasers, or other tactical gear.

The barrel itself is 4150 chrome moly vanadium with a QPQ corrosion-resistant finish inside and out—tough steel built to last through thousands of rounds. It's threaded 5/8x24 at the muzzle, compatible with most suppressors, flash hiders, and muzzle devices (the included A2 flash hider is not pinned or welded, so you can swap it easily). The gas system is rifle-length on a .750 low-profile gas block, tuned for reliable cycling with 300 Blackout's subsonic and supersonic loads. The M4E1 upper receiver features M4 feedramps, enhanced forging with a billet appearance, laser-engraved T-marks for reference, and includes the port door and forward assist. This upper does not include a bolt carrier group or charging handle—those are your choice to round out the build.

Whether you're building a short-range hunting rifle, a suppressed subsonic platform, or a compact home-defense upper, this Aero Precision assembly delivers the precision and reliability you need from a name that's earned trust across the shooting community.

Key Features

• Complete assembled upper receiver—ready to install on your lower
• ATLAS R-ONE handguard with proprietary attachment system for strength and slim profile
• Full-length top picatinny rail for optics and accessories
• Quick-disconnect sling mounts at 3, 6, and 9 o'clock positions
• 10-inch 300 Blackout barrel optimized for compact, maneuverable shooting
• 4150 chrome moly vanadium barrel with QPQ finish for corrosion resistance
• Threaded 5/8x24 muzzle for suppressors and muzzle devices
• Low-profile .750 gas block with rifle-length gas system
• M4 feedramps for reliable feeding
• Enhanced M4E1 upper receiver with billet-style forging
• Port door and forward assist installed
• A2 flash hider included (not pinned or welded)

Specifications

Frequently Asked Questions

Is this a complete upper receiver or do I need a BCG and charging handle?

This is a fully assembled upper receiver, but it does not include a bolt carrier group (BCG) or charging handle. You'll need to source those separately to complete the upper and make it functional.

Can I swap the A2 flash hider for a suppressor or other muzzle device?

Yes. The A2 flash hider that comes with this upper is not pinned or welded to the barrel, so you can remove it easily. The muzzle is threaded 5/8x24, which is standard for 300 Blackout suppressors and muzzle devices.

What's the difference between the ATLAS R-ONE handguard and a standard tube?

The ATLAS R-ONE uses Aero Precision's proprietary ATLAS attachment system, which is designed to be lighter and slimmer than traditional picatinny tube handguards while maintaining rigidity and strength. It features a full-length top picatinny rail, quick-disconnect sling mounts at 3, 6, and 9 o'clock, and is compatible with low-profile gas blocks.

What barrel length options are available for the M4E1 300 Blackout upper?

Aero Precision offers 300 Blackout barrels in 8-inch, 10-inch, and 16-inch lengths. This specific product includes the 10-inch barrel.

Is this upper compatible with mil-spec AR15 lower receivers?

Yes. The M4E1 upper receiver is compatible with standard mil-spec AR15 lower receivers. It features .250 takedown pin holes and M4 feedramps for reliable feeding.