This Rosco 10.5″ M4 5.56 NATO Bloodline Barrel is built to be the perfect addition to any SBR or pistol build. ALL NFA RULES APPLY! Rosco 5.56 (NATO) barrels are crafted to meet the needs of modern carbine shooters. Rosco is a lot different from your daddy’s Sporter AR, and those specs just won’t cut it anymore. From properly managing dwell times for SBRs, to running suppressed, or setting up a balanced patrol carbine, Rosco has included your needs in its design. Rosco has achieved this by selecting the right twist rates, gas port sizes, and barrel materials suited for each barrel.