This Rosco 12.5″ M4 5.56 NATO Bloodline Barrel is designed to be the perfect addition to any SBR or Pistol build. The Rosco 5.56 (NATO) barrels are designed to meet the modern day carbine shooters requirements. They are a long way from their 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 they have incorporated your needs into their engineering. They have successfully accomplished this by picking the right twist rates, gas port diameters, and barrel materials according to the barrel they are making (not a lazy blanket method). They have also balanced input from their consumers and military end users in order to bring you the product you need, not just the one they want to sell you.