One in seven inch twist improved polygonal rifling, 300 BLK Noveske Match chamber, extended feed ramps, bead blasted finish, pistol length gas system, gas tube, pinned Low Profile Gas Block, 5/8×24 threads, medium contour. Designed to run optimally firing both subsonic suppressed and supersonic unsuppressed. Barrel is tuned to lock back on the last round using subsonic 220 and 208 grain ammunition with a sound suppressor. Firearm may not lock back with subsonic 220 and 208 grain ammunition without a sound suppressor. Subsonic 300 BLK ammunition is more susceptible to a malfunction due to carbon fouling and adverse conditions than supersonic ammunition. Suppressors which cause off axis turbulence such as those with K type baffles may cause baffle strikes and/or point of impact shift and may damage your suppressor. Consult you suppressor manufacturer to determine if your suppressor is suitable for this application. Barrel installation should be performed by a qualified gunsmith. Installation of the gas block dowel pin and gas block is required to complete the assembly process. All NFA Rules Apply.