M4E1 300Blk Assm Upper Gov 10''Bbl Pistol-Length Threaded Blk

The Aero Precision M4E1 300 Blackout assembled upper receiver with 10-inch barrel is purpose-built for shooters who want a complete, ready-to-assemble upper for pistol-caliber AR builds. This upper pairs a cold-hammer-forged, mil-spec .300 Blackout barrel with Aero's M4E1 receiver platform and the lightweight ATLAS S-ONE handguard, giving you a compact, modular foundation for a short-barreled rifle, pistol, or specialty build. Whether you're running subsonic suppressed rounds, supersonic hunting loads, or just building a versatile truck gun, the 10-inch barrel strikes a balance between velocity and maneuverability.

The 10-inch barrel is forged from 4150 Chrome Moly Vanadium steel with a 1-in-7 twist rate optimized for .300 Blackout projectiles. It features a QPQ corrosion-resistant finish inside and out, a pistol-length gas system, and a 5/8x24 threaded muzzle—ready for suppressors or muzzle devices. The barrel comes with a low-profile gas block and passes HP and MPI testing. The M4E1 receiver itself showcases Aero's enhanced forging with M4 feedramps, laser-engraved T-marks, and .250 takedown pin holes; it accepts standard AR15 components and plays well with Aero's Extended Series handguards.

The ATLAS S-ONE handguard is engineered for lightweight builds: it measures 1.3 inches inside diameter (1.5 outside), features a slim profile with the center top rail eliminated to save weight, and includes M-LOK slots on front and rear picatinny rails. Quick-disconnect sling attachment points sit at 3, 6, and 9 o'clock. The handguard is compatible with low-profile gas blocks and mil-spec AR15 uppers and barrels. Note: this upper does not include a bolt carrier group or charging handle, and the muzzle threads are not pinned or welded—you have the freedom to thread on your own brake, flash hider, or suppressor.

Key Features

• M4E1 enhanced-forged upper receiver with M4 feedramps and laser T-marks
• 10-inch .300 Blackout CMV barrel with 1-in-7 twist, HP and MPI tested
• 5/8x24 threaded muzzle ready for suppressors or muzzle devices
• Lightweight ATLAS S-ONE handguard with M-LOK slots and slim profile
• Pistol-length gas system with low-profile gas block
• QPQ corrosion-resistant finish on barrel
• QD sling mounts at 3, 6, and 9 o'clock positions
• Picatinny rails on handguard front and rear

Specifications

Frequently Asked Questions

Does this upper include a bolt carrier group and charging handle?

No. This is an assembled upper receiver only. You'll need to source a bolt carrier group and charging handle separately to complete the assembly.

Is the muzzle pinned and welded?

No. The muzzle is threaded but not pinned or welded, so you can remove or swap muzzle devices as needed.

What handguard length comes with the 10-inch barrel?

The 10-inch .300 Blackout barrel pairs with a 9-inch ATLAS S-ONE M-LOK handguard.

Is this upper compatible with mil-spec AR15 components?

Yes. The M4E1 receiver and ATLAS S-ONE handguard are compatible with standard mil-spec AR15 upper receivers, barrels, and low-profile gas blocks.