Advanced Armament Corp 12.5" 300 BLK Complete Upper Receiver -New in Box

MSRP: $1,344.52
Was: $1,344.52
Now: $879.99
(You save $464.53 )

Out of stock



This Advanced Armament Corp. AR-15 Upper Receiver Assembly in 300 AAC Blackout is a pin-on, ready-to-shoot top end for use with any legally registered SBR or pistol AR-15 lower receiver. The Mil-Spec 4150 chrome moly vanadium steel barrel comes equipped with 1 in 7" twist rifling, M4 feed ramps, a low profile steel gas block, and is finished inside and out with a protective black nitride treatment for superior durability and corrosion resistance. The muzzle is threaded with a 5/8"-24 pitch for easy installation of a silencer, and is topped off with an effective AAC 51T Blackout flash hider. 

The upper features a forged M4-style flat-top receiver onto which a KAC URX rail is rigidly attached. The URX creates a full length top rail surface when matched with the flat-top upper to accommodate almost any desired sighting arrangement. The heat-treated, full auto bolt carrier is finished in a slick Nickel Boron coating, and comes equipped with a properly-staked gas key and Carpenter 158 steel bolt assembly. This 12.5" 300 Blackout upper utilizes a pistol length gas system and is compatible with most subsonic and supersonic ammunition, with or without a sound suppressor in place.


  • Upper Receiver: AAC A3 Flat-Top 
  • Barrel Length: 12.5" 
  • Barrel Contour: Medium 
  • Barrel Material: 4150 Chrome Moly Vanadium Steel
  • Barrel Manufacturer: AAC
  • Muzzle Thread Pattern: 5/8"-24 
  • Chrome Lined: No 
  • Barrel Finish: Black Nitride
  • Twist Rate: 1:7"
  • Chamber: 300 AAC Blackout 
  • M4 Feed Ramps: Yes 
  • Muzzle Device: AAC 51-T Blackout Flash Hider* (Loose - See note below)
  • Gas System Length: Pistol 
  • Gas Block Diameter: 0.750" 
  • Handguard: KAC URX rail 
  • Sights: None 
  • Bolt Carrier Assembly Included: Yes 
  • Bolt Carrier Type: Mil-Spec, Nickel Boron Finish

* The AAC 51-T Blackout Flash Hider was left loose by the assembler at AAC per customer's order request.

What's in the Box:

  • 1X AAC 12.5" 300 BLK Complete Upper Receiver with KAC URX Rail
  • 1X AAC Nickel Boron Complete Bolt Carrier Group
  • 1X Mil-Spec AR15 Charging Handle
  • 1X Original Purchase Receipt
  • 1X Original Packing Slip


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