Fightlite Industries 5.56x45mm NATO Black Mag Phosphate. 56x45mm NATO Black Mag Phosphate - Complete barrel assembly for use with MCR rifles and upper receiver assemblies. Includes barrel extension with fixed headspace gas block assembly 4 position regulator piston flash hider and dovetail cover. Specifications for FightLite BBL006 5.56x45mm NATO Black Mag Phosphate: Manufacturer: FightLite Finish: Mag Phosphate Gas System Length: Mid Length Additional Features: 1-7in. Twist Adjustable FightLite BBL006 5.56x45mm NATO Black Mag Phosphate