This Rosco 300 Blackout (300 BLK) barrel was designed for SBR and Pistol use in conjunction with suppressors. The 300 Blackout Rosco barrel was made to be a direct replacement for any MK 18 platforms that are currently in 5.56 NATO. The barrel is also perfect for carbines which require a slightly longer rail in order to run PEQ-15's, D-BAL (series), or any laser aiming devices comfortably. All NFA rules apply Features11 Degree barrel crownNitride Barrel and barrel extension4150 CMV materials