Mil.-spec certified 4150 chrome-moly vanadium steel M4 contour barrel with 1/7 twist Chambered in 5.56 x 45mm NATO MELONITE coated barrel T-marked forged M4 upper receivers with extended M4 feed ramps Picatinny gas block A2 flash hider installed with Peel washer M4 single heat shield handguard M16 bolt carriers Mil.-spec fire control group with .154-diam. pins Mil.-spec .154-diam. hammer and trigger pins Mil.-spec .250-diam. take-down pins Mil.-spec 6-position ribbed reinforced stock Quad Rail 30-rd. polymer Pmag. Kit: 6 1/2 lbs. 16"l. barrel.