The URX 4 is Knight’s latest rail system offering, utilizing a one piece design with an Integral Barrel Nut (IBN). The top of the anodized aluminum URX 4 features a STANAG rail, while the other sides accept KeyMod modular accessories. The URX 4 includes two steel QD inserts located at 3 and 9 o’clock on the rear of the forend.
Installation is simple. The barrel is seated in the upper and the rail tightened into place. A series of provided shims (similar to those provided with various muzzle devices) is used to index the rail at top dead center. Knight’s supplies a proprietary wrench to torque the rail into place.
I like the handling characteristics of the URX 4. I normally only run a light (9 o’clock) and IR-laser (12 o’clock) on my carbines. The remaining rail surfaces on typical four rail forend systems add weight without seeing use. The Knight’s URX 4 is lighter and slicker. For instance, my Daniel Defense 12.5″ RIS 2 weighs in at 19.4 ounces versus the 13″ URX 4 at 12.7 ounces!