This Rosco 12.5″ M4 5.56 NATO Bloodline Barrel is designed to be the ideal addition to any SBR or pistol build. The Rosco 5.56 (NATO) barrels are built to meet the needs of modern carbine shooters. They are a far cry from their predecessor’s Sporter AR, and those specs just won’t suffice anymore. From properly managed dwell times for SBRs to running suppressed or setting up a balanced patrol carbine, they have integrated your needs into their engineering. They have achieved this by selecting the right twist rates, gas port diameters, and barrel materials tailored to each barrel (not a lazy, one-size-fits-all approach). They also incorporate feedback from their consumers and military end users to deliver the product you need, not just the one they want to sell.