Concept Development Corporation Sitelite SL-150 Ultra Mag Professional Laser Boresighter VZSL150. Super-strong magnets in the arbor securely centers the laser in the muzzle for consistent accuracy. Adapters and O-rings fit all .22- .50 caliber handguns and rifles; 20- and 12-gauge shotguns and muzzleloaders. No metal touches the rifling of your firearm. To boresight place the target 25 feet from the muzzle and center the laser on the target. Dial in the scope's crosshairs and you're boresighted for 100 yards Package Contents: Concept Development Corporation Sitelite SL-150 Ultra Mag Laser Boresighter Concept Development Corporation VZSL150: Sitelite SL-150 Ultra Mag Professional Laser Boresighter