MPN: APAR700305M51 / APAR700705M51


  • Caliber: .223 Rem / 5.56 NATO
  • Chamber: .223 Wylde
  • Finish: Type III Class 2 Hardcoat Anodized Finish
  • Upper Receiver: Aero Precision M4E1 Threaded Upper - 7075-T6 Aluminum
  • Handguard: 15-Inch ATLAS S-ONE or R-ONE M-LOK Handguard of choice
  • M4 Feed Ramps: Yes
  • Muzzle Device: A2 Flash Hider
  • Barrel: 18" 1:8 Twist 416R Stainless Steel Fluted Barrel
  • Muzzle Thread Pattern: 1/2"-28 TPI
  • Gas Block: Aero .750" Low-Profile Gas Block
  • Gas Tube: Rifle-Length Gas Tube
  • Bolt Carrier Group: Not Included
  • Charging Handle: Not Included
  • HP and MPI Tested

*This upper assembly does not come with Bolt Carrier Group and Charging Handle

*ATLAS S-ONE Handguard: Front and rear Picatinny rail section. Eliminated center of top rail for weight reduction.

*ATLAS R-ONE Handguard: Full top Picatinny rail


  • Weight: ~3.5 lbs.
  • Overall Length: ~26.44"


  • AR-15 lower receivers


  • 1x Aero Precision 18" Fluted .223 Wylde M4E1 Complete Upper Assembly


If you are building an AR-15 rifle, you need to check out the M4E1 Complete Upper Assembly from Aero Precision. This upper assembly is available in multiple calibers and configurations. However, this one has a .223 Wylde hybrid chamber, which means it can safely fire both 5.56 and .223 Remington rounds.

This complete upper features an 18'' fluted barrel made from 416R Stainless Steel; it is a very light barrel, and the fluted design increases its surface area, which is better for heat dissipation. The barrel has a 1:8 twist rate rifling and is threaded with a 1/2"-28 TPI thread pitch. It comes equipped with an A2-style flash hider as well.

This upper assembly used a low-profile gas system with a rifle-length gas tube, which is ideal for an 18-inch long barrel.

You can choose between two different handguards, either the Aero Precision ATLAS S-ONE or R-ONE M-LOK Handguard, both of which will be 15 inches long. They have M-LOK slots on both sides and the bottom and use anti-rotation pins to mount on the receiver. However, the R-One handguard has a full-length Picatinny top rail, whereas the S-One has two small sections of Picatinny top rail on the front and rear of the handguard.

The M4E1 receiver is made from 7075-T6 Aluminum and features a forward assist and port door. It also has M4 feed ramps for better reliability.

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  • This Item: Aero Precision 18" Fluted .223 Wylde M4E1 Complete Upper Assembly
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    MSRP: $750.00
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