You'll need to test fire at various ranges to find out what the various aiming points/crosshairs correspond to. The longer the range, the further off the graduations will be. Once you know the distance each crosshair is zeroed at, you're all set. Really, you should do that even with a rifle in .308...the markings are a general guide, but can't be exactly dead-on for every load/bullet weight/barrel length even in the cartridge they're calibrated for.