Bloodline 5.5"" 9mm Barrel: This Rosco 5.5"" 9mm Barrel was primarily designed for suppressed carbines/ pistols where the handguard will be ran over the rail. It will give you the flexibility of running a suppressed platform that offers the most compact size possible without sacrificing performance. Twist rates have also been taken into account in order to optimize performance for a multitude of rounds that you may also be running out of your duty/ concealed carry pistol in order to allow a ""cross platform"" ballistic familiarity. ALL NFA RULES APPY! Rosco 9mm barrels are perfect for sub-caliber carbine platforms. Rosco has taken the time to understand the purpose for these platforms and design a barrel which will support it effectively. It is the goal to get you the performance that you seek out of these barrels whether you are running suppressed"" defense ammo"" sub-sonic ammo or supersonic ammo (depending on barrel length). Twist rates"" and lengths have all been taken into account when Rosco sets out to make these barrels.