Aero Precision M4E1 Threaded Barreled AR-15 Upper 5.56 Carbine Atlas R-One – 12.5″


  • 12.5” 5.56 barrel
  • 4150 CMV barrel
  • HPT and MPI
  • Salt bath Nitride finish
  • 1:7 twist rate
  • Carbine length gas system
  • M4E1 Enhanced forged 7075-T6 upper
  • Hardcoat anodized
  • Laser engraved T-marks
  • Scalloped picatinny top rail
  • Built in anti-rotation tabs
  • M-LOK slots
  • Does not include BCG or charging handle


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SKUAPAR700704M30 Category

Note: This barreled upper receiver assembly has a barrel length under 16” and is therefore subject to all NFA rules and regulations. Know your local laws before purchasing.

Looking to build the perfect AR-15? The Aero Precision M4E1 Threaded Barreled Upper Receiver is the perfect place to start. Forged from 7075-T6 aluminum and precision machined to M4E1 specs, this upper receiver is designed for use with standard barrel nut systems. It’s matte black hardcoat anodized and features laser engraved T-marks on the upper picatinny rail, making it easy to add your favorite optics or other accessories. This 12.5″ 5.56 barreled upper comes with the Atlas R-One M-LOK free float handguard with full length picatinny top rail. The handguard is slime 1.3″ in diameter.

The Aero Precision M4E1 Threaded Barreled AR-15 Upper 5.56 Carbine Atlas R-One is the perfect choice for those who want a versatile and high-performance upper for their AR-15. This upper features a 12.5” barrel machined from 4150 Chrome Moly Vanadium steel with a salt bath Nitride finish, providing exceptional durability and corrosion resistance. The pistol length gas system provides reliable cycling of the action, while the 1:7 twist rate is ideal for heavier bullets. The M4 feed ramp barrel extension ensures reliable feeding of rounds, and the entire assembly is magnetic particle inspected and high pressure tested for superior quality control.


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