The XX was designed specifically for the Cheytac cartridges. This is Designed for use on .308 Winchester rifles, the APA Gen XX Bastard Muzzle Brake is machined from stainless steel and features a polished finish. After great success with our XXX it was requested that we design a brake specifically for these cartridges and their slightly smaller barrels. The Gen 2 has a nut that is a separate piece. This allows our customers to install the brake themselves at home if they already have a threaded barrel. Installations takes about 30 seconds and has no hideous crush washers or peel washers to deal with. Additionally competitive shooters can easily remove this brake for cleaning or simply to move if from barrel to barrel. We recommend a muzzle diameter of 1.0 - 1.3 inches for this brake. APA Gen II XX Bastard Muzzle Brake 7/8x24 .308 Stainless Steel