The Product is precisely engineered to fit into the chamber, ensuring exact and consistent laser alignment with the bore. Perfect for hunters, competitive/recreational shooters and law enforcement. Save time, money and frustration. Convenient, accurate and easy to use. Compact, lightweight and durable. Type: Visible Red Laser. Operation: On/Off End Cap Laser. Battery: 3 x AG13/LR44 (included). Laser wavelength: 635-655nm. Total Length: 60.76mm (2.39" approx). Diameter: 20.32mm (0.8" approx). Color: Red. How to use: Turn on the bore sight by turning bottom of bore sighter clockwise. Load the laser into the chamber as if it was a normal round. Place the dot on a target downrange. Align your sights cross hairs or dot with the projected spot. From there, you can adjust your scope or sights without ever wasting ammo! Turn off bore sighter by turning bottom of unit counter clockwise until dot no longer appears, or take out batteries completely for longest battery life.