Burris FastFire Red-Dot Reflex Sight ( 4 MOA Dot Reticle) The FastFire dramatically increases speed and accuracy. It simplifies the act of aiming, eliminating the need to focus on and align the front sight, rear sight and target. With the FastFire, the aiming red dot and target are always in focus and properly aligned for the ultimate in accuracy. The FastFire II provides the only fully waterproof unit in its product category. The FastFire sight is very small, mounts very low, and weighs a mere 1.6 ounces. And it has repeatedly proven it’s toughness on the slides of high power semi-autos, on slug guns, on shotguns and on high power rifles. The FastFire housing is made of metal for strength and durability. It’s lenses are precision ground and polished to exacting geometries to virtually eliminate parallax and to provide a very clear crisp sight picture. It is fully windage and elevation adjustable and lockable. It features both an on/off switch and a light sensor that automatically adjusts the dot’s brightness to the available light. The included plastic hood covers the light sensor and puts the unit in sleep mode when the on/off switch is set to “on.” FastFire is powered by a lithium CR2032 battery, which is commonly available and long lasting because of the highly efficient electronics and the battery-saver mode. A battery can last as long as five years . Special bases are available for the most common firearms.