The FastFire 3 is the best selling red dot sight from Burris. 8 MOA dot.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 settingsBattery access is conveniently located on the top of the sight; automatic time-out feature after 8 hours helps battery last up to 5 yearsAvailable with Picatinny/Weaver mount for mounting on rifles, handguns and tactical shotguns