The Aero Precision M4E1 in .300 BLK uses the same enhanced upper receiver platform as the 5.56x45mm model with a 16-inch barrel optimized for subsonic and supersonic .300 BLK performance. The M4E1 upper design provides a tight barrel nut interface for accuracy. Type: Semi-Auto Rifle Action: Direct Impingement Caliber: .300 BLK Capacity: 30 Year introduced: 2016, USA Weight: 6.8 oz Overall length: 32.5" Status: Active Intended use: Suppressor Host, Home Defense, Range