Recently, Picatinny rails with 20 minutes of gain have become a popular accessory for long-range rifles. Such a rail is machined with a slant up in the rear, to tip the scope down in front. Because inside the scope’s erector assembly is tilted, too, your sight line meets the bullet path closer to the rifle and puts the second intersection farther away. The 20-minute shift (20 inches at 100 yards) allows you to zero at very long range without running out of elevation adjustment. Essentially, it raises point of impact without your having to spin the elevation dial for the first 20 minutes of lift. Not cranked to the limit of its adjustment range, the erector assembly is more nearly centered in the scope, so your sight line is close to lens centers for the best target image.