GSM End of Barrel Laser Boresight - Basic For use on .17 to .50 caliber and 10, 12 & 20 gauge shotguns Includes Calibration Target and Carrying tube Green lasers project brighter and are highly visible at long distances End Of Barrel Laser Bore Sighting Systems Patented design Durable machined aluminum construction Unit includes (3) three LR44 Alkaline button cell batteries No metal on metal contact, will not scratch the finish of the barrel or damage your rifling