This 9mm chambered 11 inch Modern Series Barrel is machined from 4150 Chrome Moly Vanadium steel with a QPQ Corrosion Resistant Finish and 1/2-28 x .620 full profile threads. Designed to work with both Colt/RR and Glock style AR builds. Compatible with standard mil-spec uppers. There are also numerous dedicated 9mm upper options that work. Requires the use of a unique magwell conversion (Colt/Rock River style) with UZI mags or a dedicated 9mm lower with Glock mags. 9mm on an AR15 platform operates by blowback and does not need a gas block or gas tube.