The latest AimShot 223 20x modular laser bore sight with Modular Battery Pack. This version of their proven 223 laser bore sight adds the modular battery pack that allows you to remove the small watch batteries and end cap (included) and replace with it with an external battery pack that contains 2 AAA batteries (included) that will give you run times of 20+ hours for your laser bore sight. The 20X designation is for the brighter red laser that is easier to see over long distances or in full sunlight. 632nm wavelength red laser is more visible to the human eye and is brighter. The latest modular bore sight includes BOTH the smaller watch batteries and end cap, as well as the latest external battery pack that runs on 2 AAA batteries for 20+ hours of laser run time. The external battery pack has a small magnet on the side to hold it to the receiver and allow you extra time to get your optics dialed in and a small switch on the back of the battery case that allows you to turn the unit on and off easily.