Chamber the Sightmark 300BLK (7.62x35mm) Boresight in your rifle like a regular cartridge and a red laser dot shows exactly where you're aiming. Range for sighting is 15-100 yards, with an operating temperature at -10 to 50 F/C. Ideal for hunters, competitive shooters and law enforcement, this device significantly reduces wasted cartridges and shells. Includes a carrying case and three AG3 batteries.