AeroPrecision167529639
M4E1 300Blk Assm Upper Gov 10''Bbl Pistol-Length Threaded Blk$590.98
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Availability: In Stock
Current Stock: Out of stock
The Aero Precision M4E1 .300 Blackout assembled upper with 8-inch barrel is a complete, ready-to-run upper receiver built for shooters who prioritize compact size and lightweight handling. Chambered in .300 Blackout with a 1:7 twist rate, this upper pairs a 4150 CMV barrel—finished with a QPQ corrosion-resistant coating—with Aero's ATLAS S-ONE handguard system, a slim-profile M-LOK rail designed to shed weight without sacrificing strength or utility. The 8-inch barrel length and pistol-length gas system make this an excellent choice for short-range shooting, suppressed fire, or compact builds where maneuverability matters. This is a complete upper receiver assembly ready to mate with your lower—you'll just need to source a bolt carrier group and charging handle separately.
The M4E1 enhanced forging gives the upper a refined appearance while maintaining the durability Aero Precision is known for. The ATLAS S-ONE handguard strips weight through intelligent design: it eliminates the center of the top rail, keeps the profile slim at 1.3 inches inside diameter, and still delivers front and rear picatinny rails plus M-LOK mounting along the sides. Quick-disconnect sling points at 3, 6, and 9 o'clock give you flexibility for how you carry and deploy. A low-profile gas block and pistol-length gas tube come installed, and the muzzle features a 5/8x24 thread for suppressors or brakes—though the included brake is not pinned or welded, so you can swap it as needed.
Built from the ground up to be a cohesive system rather than a collection of mismatched parts, the M4E1 upper handles .300 Blackout's subsonic potential and delivers the compact footprint modern shooters expect. The 8-inch barrel weighs just 18 ounces and has been HP and MPI tested to verify integrity. If you're building a short-range workhorse or an integrally suppressed AR pistol, this upper gives you a proven platform without guesswork.
| Brand | Aero Precision |
| Product Type | Assembled Upper Receiver |
| Caliber | .300 Blackout |
| Barrel Length | 8 inches |
| Barrel Material | 4150 Chrome Moly Vanadium |
| Barrel Finish | QPQ Corrosion Resistant |
| Twist Rate | 1 in 7 |
| Muzzle Thread | 5/8x24 |
| Gas System | Pistol Length |
| Gas Block Journal | .750 inch |
| Gas Port Size | .109 inch |
| Barrel Weight | 18 ounces |
| Handguard | ATLAS S-ONE M-LOK |
| Handguard Inside Diameter | 1.3 inches |
| Handguard Outside Diameter | 1.5 inches |
| Barrel Extension | M4 HP and MPI Tested |
| Includes | Upper receiver, barrel, handguard, low-profile gas block, gas tube, port door, forward assist, muzzle brake (not pinned/welded) |
| Does Not Include | Bolt carrier group, charging handle |
This is a complete upper assembly—it includes the receiver, barrel, handguard, and gas system. To finish the build, you'll need to add a bolt carrier group and charging handle. You'll also need a lower receiver, magazine, and fire control group to create a complete firearm. Check local and federal laws before assembling.
Yes, the muzzle brake comes installed on the 8-inch barrel. It is not pinned or welded, so you can remove it and install a suppressor, flash hider, or other muzzle device with a 5/8x24 female thread. If you plan to use a suppressor, verify it is rated for .300 Blackout and that your build complies with federal and local regulations.
Yes, the M4E1 upper is compatible with mil-spec AR15 lower receivers. The .250 takedown pin holes and standard M4 feedramps ensure drop-in fitment with any standard lower platform.
The ATLAS S-ONE is Aero Precision's lightweight handguard, designed with weight savings as a priority. It eliminates the center of the top rail (which many shooters don't use) to reduce overall mass while maintaining front and rear picatinny rails and full M-LOK support on the sides. It includes QD sling sockets at multiple points and is compatible with low-profile gas blocks, making it ideal for compact and lightweight builds.
SKU: 167527234 • Weight: 3.02oz
Availability: In Stock
Current Stock: Out of stock
The Aero Precision M4E1 .300 Blackout assembled upper with 8-inch barrel is a complete, ready-to-run upper receiver built for shooters who prioritize compact size and lightweight handling. Chambered in .300 Blackout with a 1:7 twist rate, this upper pairs a 4150 CMV barrel—finished with a QPQ corrosion-resistant coating—with Aero's ATLAS S-ONE handguard system, a slim-profile M-LOK rail designed to shed weight without sacrificing strength or utility. The 8-inch barrel length and pistol-length gas system make this an excellent choice for short-range shooting, suppressed fire, or compact builds where maneuverability matters. This is a complete upper receiver assembly ready to mate with your lower—you'll just need to source a bolt carrier group and charging handle separately.
The M4E1 enhanced forging gives the upper a refined appearance while maintaining the durability Aero Precision is known for. The ATLAS S-ONE handguard strips weight through intelligent design: it eliminates the center of the top rail, keeps the profile slim at 1.3 inches inside diameter, and still delivers front and rear picatinny rails plus M-LOK mounting along the sides. Quick-disconnect sling points at 3, 6, and 9 o'clock give you flexibility for how you carry and deploy. A low-profile gas block and pistol-length gas tube come installed, and the muzzle features a 5/8x24 thread for suppressors or brakes—though the included brake is not pinned or welded, so you can swap it as needed.
Built from the ground up to be a cohesive system rather than a collection of mismatched parts, the M4E1 upper handles .300 Blackout's subsonic potential and delivers the compact footprint modern shooters expect. The 8-inch barrel weighs just 18 ounces and has been HP and MPI tested to verify integrity. If you're building a short-range workhorse or an integrally suppressed AR pistol, this upper gives you a proven platform without guesswork.
| Brand | Aero Precision |
| Product Type | Assembled Upper Receiver |
| Caliber | .300 Blackout |
| Barrel Length | 8 inches |
| Barrel Material | 4150 Chrome Moly Vanadium |
| Barrel Finish | QPQ Corrosion Resistant |
| Twist Rate | 1 in 7 |
| Muzzle Thread | 5/8x24 |
| Gas System | Pistol Length |
| Gas Block Journal | .750 inch |
| Gas Port Size | .109 inch |
| Barrel Weight | 18 ounces |
| Handguard | ATLAS S-ONE M-LOK |
| Handguard Inside Diameter | 1.3 inches |
| Handguard Outside Diameter | 1.5 inches |
| Barrel Extension | M4 HP and MPI Tested |
| Includes | Upper receiver, barrel, handguard, low-profile gas block, gas tube, port door, forward assist, muzzle brake (not pinned/welded) |
| Does Not Include | Bolt carrier group, charging handle |
This is a complete upper assembly—it includes the receiver, barrel, handguard, and gas system. To finish the build, you'll need to add a bolt carrier group and charging handle. You'll also need a lower receiver, magazine, and fire control group to create a complete firearm. Check local and federal laws before assembling.
Yes, the muzzle brake comes installed on the 8-inch barrel. It is not pinned or welded, so you can remove it and install a suppressor, flash hider, or other muzzle device with a 5/8x24 female thread. If you plan to use a suppressor, verify it is rated for .300 Blackout and that your build complies with federal and local regulations.
Yes, the M4E1 upper is compatible with mil-spec AR15 lower receivers. The .250 takedown pin holes and standard M4 feedramps ensure drop-in fitment with any standard lower platform.
The ATLAS S-ONE is Aero Precision's lightweight handguard, designed with weight savings as a priority. It eliminates the center of the top rail (which many shooters don't use) to reduce overall mass while maintaining front and rear picatinny rails and full M-LOK support on the sides. It includes QD sling sockets at multiple points and is compatible with low-profile gas blocks, making it ideal for compact and lightweight builds.
SKU: 167527234 • Weight: 3.02oz