What's in the Box Colt AR15A4 5.56mm Semi-Automatic Rifle (1) 30-Round Magpul Magazine Cable Lock Owner's Manual This Semi-Automatic Colt Rifle is a throwback to the full size AR-15 which gave birth to the Modern Sporting Rifle. The Colt AR15A4 is defined by it's 20" 1:7 Twist Government Profile Chrome Lined Barrel and A2 Fixed Buttstock. Manufacturer: Colt Model: AR15A4 Caliber: 5.56x45mm NATO Capacity: 30+1 Barrel: 20" Chrome-Lined Barrel Overall Length: 39.5" Upper Receiver Material: 7075-T6 Aluminum Upper Receiver Finish: Black Hardcoat Anodized Barrel Material: 4150 CMV Barrel Finish: Manganese Phosphate Barrel Twist Rate: 1:7" RH Grooves: 6 Grooves Lower Receiver Material: 7075-T6 Aluminum Lower Receiver Finish: Black Hardcoat Anodized Front Sight: A2 Fixed Front Sight Rear Sight: Detachable Carry Handle Trigger Type: Single Stage Grip: Government A2 Grip Operating System: Direct Gas Impingement