The Colt SP1 was the original civilian AR-15, introduced in 1964 as the semi-automatic counterpart to the military M16. It featured a triangular handguard, fixed A1 carry handle, and a 20-inch barrel with a 1:12 twist rate optimized for 55-grain bullets. Type: Semi-Auto Rifle Action: Gas-Operated Caliber: 5.56x45mm Capacity: 20 Year introduced: 1964, USA Weight: 7.6 oz Overall length: 39" Status: Discontinued Intended use: Range, Collecting