CMMG's Barrel Sub-Assembly is ideal for building your custom AR-15 upper group. It comes with properly installed M4 barrel extension. The barrel is constructed of 4140 chrome moly with a slat bath nitride finish and 5/8x24" threads.
Specifications:

Caliber or Gauge	300 AAC Blackout/Whisper (7.62x35mm)
Length	16.1"
Model	Barrel Sub-Assembly
Twist	1:7"
Sights	None
Bore Type
Finish	Black Nitride
Type	Rifle
Chokes Included
Choke Configuration
Barrel Type	Carbine Length
Ammo Type
Barrel Features	Multi Role Profile