The Sons of Liberty Gun Works M4-L89 Barreled Upper is a professional-grade, non-NFA upper receiver group optimized for use with Huxwrx Flow-series suppressors. It features a 14.5-inch Liberty Fighting Barrel with a Pin and Welded (P& W) Huxwrx Flash Hider, which brings the permanent overall length to the legal 16-inch requirement for standard rifles. The foundation of this build is the L89 Drivelock handguard, featuring a titanium barrel nut and a high-strength locking interface to ensure that rail-mounted lasers and optics maintain a precise zero under thermal stress or hard use. This configuration utilizes a mid-length gas system, providing a balanced and reliable recoil impulse that is particularly effective when shooting suppressed. Sons of Liberty Gun Works M4-L89 5.56mm 14.5" Bbl Mid Gas L89 Rail P& W HUXWRX Mount Liberty Fighting Bbl & Mil-Spec Upper Receiver U-M4L89-556-145-HUX