We had these made for us with a pinned FSB using a Triangle Handguard Cap. This means that this barrel is compatible with most drop-in handguards. We also pinned a BCM A2X Flash Hider to extend this barrel out to 16.Barrel SpecsBrandBallistic AdvantageLength14.5Chamber5.56 NATO (shoots both 5.56 NATO and .223)ProfileGOVT / SOCOMFinishQPQ NitrideBarrel Steel4150V Chrome MolyTwist Rate1:7Gas System LengthMid-LengthGas Block Journal.750Feed Ramp ExtensionM4Muzzle1/2 X 28Weight27ozAll 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 permanently attaching a muzzle device extending the length to 16 inches.