Rosco Manufacturing Bloodline Heavy Barrel, 300BLK, 16, Black Nitride Finish, 1:7 Twist, 5/8x24, 4150 CMV BL-16-HB-300BLK-8-P This Rosco 16" 300 Blackout (300 BLK) barrel is perfectly suited for carbines shooters that plan on running only supersonic ammo" or are building a well-balanced hunting platform. Rosco 300 Blackout barrels were created by using input from SOCOM end users and some of the original creators of the 300 Blackout caliber. Every barrel was designed to optimize the original role for this caliber; to be suppressor friendly and accurate. It is Rosco's goal to get you the performance that you seek out of these barrels when running sub-sonic ammo or supersonic ammo (depending on barrel length). Twist rates" gas port diameters" and lengths have all been taken into account when we set out to make these. Let's just say that we don't like leaving things to chance.