Aim Sports 20 Ga Red Laser Bore Sighter. Boresighter system fits into the chamber of your shotgun and projects a red laser beam from the bore for sighting in scopes, red-dots and iron sights without firing a shot. Laser and batteries are contained inside the cartridge. Cartridge contains a 5mw red laser and uses 3- LR44/AG13 batteries. Unit turns on when batteries are inserted and turns off when batteries are removed. Insert the cartridge into the chamber, gently close the action, and aim at a target 20-30 yards away and begin sighting in.