The 9" and 12.5" barrel each feature a 1 in 7" twist and is threaded 5/8"-24 at the muzzle. These barrels include the 51T Flash Hider designed to effectively eliminate muzzle flash and works in conjunction with AAC's improved ratchet mount sound suppressors. It utilizes a pistol length gas system and is compatible with most subsonic and supersonic ammunition, with or without a silencer in place. However, some subsonic ammunition may not always cycle reliably under adverse conditions or in a severely fouled firearm without a sound suppressor attached to provide extra backpressure. Barrel assembly includes a pistol gas tube, low profile steel gas block, barrel extension and locator pin. Requires barrel nut for installation (not included).
Please Note: An “AR-15 Pistol” upper assembly has a barrel less than 16” in length. Pistol uppers are only for use on AR-15 pistol lowers and legal Short-Barreled Rifles. Other configurations may violate Federal law.