I used that same scope and mount on a Remington 700 with a 20 minute rail and it worked just fine, so I don't think the AR has a 20 minute rail. The main difference between the Rem. 700 and this AR was probably more the speed of the bullet. The Remington was spitting out the 105 grain 6mm bullets at about 2800 feet per second and they were VLD bullets. These Barns bullets are not VLD and they are traveling around 2500 FPS. That mount, "not the rail" has Zero angle built in as far as I know, but I can check with Leupold to make sure.