Harrington & Richardson 733 Complete 11.5" Upper, Black

Caliber: 5.56 NATO
Barrel Length: 11.5"
Barrel Profile: Pencil
Barrel Steel: 4150 Chrome Moly Vanadium
Barrel Finish: Parkerized
Chrome Lining: Yes
Muzzle Thread Pattern: 1/2" x 28
Twist Rate: 1 in 7"
Barrel Extension: M4
Gas System Length: Carbine
Diameter at Gas Block: .625"
Gas Block Type: Rifle Height Front Sight Base
Muzzle Device: A2 Flash Hider
Receiver Material: Forged 7075-T6
Upper Receiver Type: C7, Feedramps
Handguard Type: Carbine, 6 hole, with heat shields
Bolt Material: Carpenter 158 Steel
Bolt Carrier Profile: Full Auto