The Adams Arms P1 model includes Adam's Picatinny Railed Gas Block with 3 adjustable settings and M4-style furniture. The P1 is your Piston Driven foundation ready to be customized to fit your needs.Specifications: Upper Receiver: A4 Flat-Top Forged Barrel Length: 16a ^2 Barrel Contour: M4 Barrel Material: 4150 Chrome Moly Vanadium Steel Muzzle Thread Pattern: 1/2a ^2-28 Chrome Lined: No Barrel Finish: QPQ Melonite / Black Nitride Twist Rate: 1 In 7a ^2 Chamber: 5.56x45mm NATO M4 Feed Ramps: Yes Bolt Carrier: Full-Auto Rated 1-Piece W/Integral Piston Strike Face Muzzle Device: A2 Flash Hider Gas System Length: Carbine Short Stroke Piston Operated Gas Block Diameter: 0.750a ^2 Handguard: M4 Handguards Sights: None Grip: A2 Grip Trigger: Standard G.I. Stock: 6-Position Collapsible Weight: 6.2 Lbs OAL: 32.5a ^2 Collapsed Lifetime Warranty: Yes