William, the Armalite Barrel is 4150 Chrome Moly Vanadium

Barrel material: Double-lapped chrome moly vanadium MIL-B-11595-E with M2023 stepdown; threaded 1/2 x 28
Upper receiver: Forged 7075-T6 aluminum flat-top with MIL-STD 1913 rail
Lower receiver: Forged 7075-T6 aluminum
specs Armalite® Defensive Sporting Rifle 15F 5.56 NATO/.223 Remington Semi-automatic AR Rifle
Each DEF15F Rifle comes standard with double-lapped, chrome-lined barrel for superior accuracy, collapsible stock for custom length-of-pull, and flash suppressor. In the Era of AR Innovation, Armalite will not be outdone in quality OR value!
Lightweight…just 6.35 lbs.
High-quality double-lapped chrome moly vanadium barrel shoots great and keeps fouling to a minimum
Barrel is 1/2 x 28 threaded, and includes a thread protector
MIL-STD 1913 rail on the receiver for optics
Includes one 30-rd. magazine
Backed by the Armalite Limited Lifetime Warranty
Order today!
Key Specifications
Item Number: 644992
Caliber: 5.56 NATO/.223 Remington
Action: Semi-automatic
Capacity: 30+1
Barrel length: 16"
Barrel material: Double-lapped chrome moly vanadium MIL-B-11595-E with M2023 stepdown; threaded 1/2 x 28
Barrel twist: 1:7" RH
Stock: Collapsible
Upper receiver: Forged 7075-T6 aluminum flat-top with MIL-STD 1913 rail
Lower receiver: Forged 7075-T6 aluminum
Sights (front / rear): Optics-ready
Trigger: Single stage
Muzzle device: Flash suppressor
Overall length: 32-35.25"
Overall weight: 6.35 lbs.
Mfg. Number: DEF15F
UPC: 651984014264