The FastFire 3 is the best selling red dot sight from Burris. It is available with a 3 MOA or 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. Product Features 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