Rosco Manufacturing Bloodline Heavy Barrel, 556NATO, 16, Black Nitride Finish, 1:7 Twist, 1/2x28, 4150 CMV BL-16-HB-556-7-C Rosco's Bloodline 16" 5.56 Heavy Barrel: This Rosco 16" 5.56 Heavy Barrel (HB) was made to cater to end users who need to run their guns hard without any remorse. The heavy contour barrel is well suited for full auto use and abuse. Rosco 5.56 (NATO) barrels are designed to meet the modern day carbine shooters requirements. We are a long way from our daddy's Sporter AR" and those specs just won't cut it anymore. From properly managed dwell times for SBR's" to running Suppressed" or setting up a balanced patrol carbine Rosco incorporated your needs into our engineering. Rosco has successfully accomplished this by picking the right twist rates" gas port diameters" and barrel materials according to the barrel. Rosco also balanced input from our consumers and military end users in order to bring you the rifle barrel you need" not just the one we want to sell you.