This .300 Blackout chambered 9 inch 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.