The M4A1 is the special operations variant of the M4, featuring a full-auto trigger group instead of burst, a heavier SOCOM profile barrel, and an ambidextrous selector. Standard weapon of Army Special Forces, Rangers, and Delta Force. The most capable M4 variant. Type: Semi-Auto Rifle Action: Gas-Operated Caliber: 5.56x45mm Capacity: 30 Year introduced: 1994, USA Weight: 6.5 oz Overall length: 29.8" Status: Active Military use: Yes Intended use: Military, Special Operations, Duty