Modular Battery Pack upgrade for existing AimShot BS9 9mm laser bore sights. Instead of using the 3 small watch batteries, this allows you to upgrade to the external battery pack that utilizes two AAA batteries and will run the red laser for 20+ hours. Fits all AimShot BS9 laser bore sight models. Also a replacement in case something happens to your existing MBS9 laser bore sight. This is just the replacement battery box and end cap for the BS9 laser bore sight or an upgrade to your BS9 for longer battery life.
Normally the external battery box version will not work well with most pistol bore sight applications. Unless the barrel is fixed in place and you can leave the action open to bore sight (pistol caliber carbines, AR15 in 9mm, single shot pistol/rifles, etc) you will need to use the standard BS9 bore sight.