American Tactical Imports Mil Sport Complete Ar-15 Upper 5.56 7.5" Black. 56x45mm 7.50" Black Nitride Barrel - Specifications for ATI ATI15MS556ML7 MilSport 5.56x45mm 7.50" Black Nitride Barrel: Manufacturer: American Tactical Imports Caliber: 5.56x45mm NATO Barrel Length: 7.5 in Gas System Length: Pistol Length Barrel Twist Rate: 1-7 Firearms Threads Per Inch: 1/2x28 Handguard Type: Free-Float Muzzle Device: Flash Hider Finish: Black Nitride Color: Black Fabric/Material: 7075-T6 forged aluminum Gun Rail: M-LOK Gun Type: Rifle Gun Make: AR Platform Gas System Type: Direct Impingement Magazine Included: No Additional Features: 1-7in. Twist ATI ATI15MS556ML7 MilSport 5.56x45mm 7.50" Black Nitride Barrel