Axeon 2218608 2nd Zero Rail Mount Standard R320B 50mm-56mm objective 330 yds Black The Axeon Second Zero is out-of-the-box weapon ready. It's the fastest way to compensate for bullet drop at extended range. The Second Zero shifts a target image up by the same number of inches a bullet drops over a specified distance. So if a bullet drops by 7 inches because of gravity, the Second Zero shifts the image up by 7". In effect, they cancel each other out. Let's say you want to hit a target at a longer distance than the 100 yards you're sighted in at. Without the Axeon Second Zero you'll have to "hold over" or "hold" above target, which means you estimate bullet drop and "hold" the crosshairs above the target by that amount. Another way to hit that further target is to physically adjust your optics to compensate for the bullet drop over the longer distance, but that can take time and can be inaccurate, or even unrepeatable. With a Second Zero made for a prescribed second distance, you don't have to calculate or adjust for hold over. It's fast, simple, and easy to use. Just flip it in place and shoot. The Axeon Second Zero is a precision optical device that gives any rifle shooter an instant additional zero distance whether in a hunting or tactical application. Its an aiming device used in conjunction with your shooting optics and works with all optical sights from rifle scopes to dot sights. The patented Second Zero, is a prism driven optical device. It will revolutionize the way you achieve accuracy at long distances. The device simply mounts forward of a traditional scope, red dot, acog, or other optic. Your optics function normally when the Second Zero is not being used. When engaged, the prisms of the Second Zero, which can be selected based on a hunters specific ammunition load, shifts the image to compensate for bullet drop. Simply place the crosshairs on the target just as you would at 100 yards.You leave your optic sighted in at 100 yards and your Second Zero provides you an additional distance depending on the load you shoot out of your rifle. Specifications: - Fits: Most Common Scope Objective Sizes Without Aobr - Type: Rail Mountbr - Size: Standardbr - Objective Size: 50mm-56mmbr - Additional Zero Distance: 330 yds.