The Colt AR-15A4 is the 20-inch commercial variant of the military M16A4 configuration, featuring a full-length upper receiver with a flat-top Picatinny rail. The 20-inch barrel provides maximum velocity and ballistic performance from the 5.56x45mm cartridge and is paired with the A2 pistol grip and stock. Type: Semi-Auto Rifle Action: Direct Impingement Caliber: 5.56x45mm Capacity: 30 Year introduced: 2000, USA Weight: 8 oz Overall length: 39.5" Status: Active Intended use: Range, Collection, Competition