Faxon Firearms 15A58M16NSQ Duty Series 5.56x45mm NATO 16" Target Crown Steel QPQ Black Nitride 4150 Steel Barrel Fits AR15/M16Faxon starts with 4150 Mil Spec steel from there, each barrel goes through a battery of tests at each operation until finished in Nitride and final inspected. All barrels are individually checked for headspace by precision custom hardened gauges. Features button rifling; Socom profile; mid barrel gas system; Nitride inside and outside finish; 1 2" 28 thread; 11 degree target crowned; 1. 1" gas block journal and M4 barrel extension.