This 5.56 NATO chambered 10.5 inch Government Profile Modern Series Barrel is machined from 4150 Chrome Moly Vanadium steel with a QPQ Corrosion Resistant Finish and QPQ coated M4 feed ramp extension. All NFA/ATF Rules Apply. You may use this barrel with a lower receiver that is a Registered SBR, Machine Gun, or Pistol. Possession of this barrel along with a Non-NFA lower receiver is Prohibited, except when installed on a Pistol configuration firearm.