Primary Weapons Systems UXR Magwell, Mag Well Cnversion Kit, For Medium Frame AR-15, Black UCRW0004-01-1F The proprietary UXR" or User XChange Rifle" is the pinnacle of firearm innovation. This revolutionary system offers unmatched modularity and performance. The patent-pending XCHANGE system allows the shooter to quickly convert to alternate calibers on the same serialized platform by exchanging just three parts - the magazine well" bolt head and barrel. To create an unparalleled shooting experience" the proprietary UXR introduces a unique bore-evacuation chamber incorporated into the barrel" along with a modified long-stroke piston system" which together allow for a smoother shot and lower recoil. From long-range precision to fast-paced shooting in dynamic environments" the UXR combines