The FastFire 3 is the best selling red dot sight from Burris. Light and tough, the FastFire 3 series puts an unmistakable, bright red dot on your target to give you an immediate speed and accuracy advantage. Can be used as a primary sight or paired on top of an existing sight. Automatic brightness sensor adjusts brightness to match the environmental conditions; also has 3 manual brightness settings. Battery access is conveniently located on the top of the sight; automatic time-out feature after 8 hours helps battery last up to 5 years. Available with Picatinny/Weaver mount for mounting on rifles, handguns and tactical shotguns. The FastFire 3 will work with virtually every "optics ready" handgun. However, the Burris supplied mounting screws may not be the correct length for every single handgun. Please contact the firearm manufacturer for specific screw lengths necessary for correct mounting.