The Holosun 510C Green Dot Reflex Sight is typically factory preset for a distance of 50 yards, and I just popped it on, did a laser bore sight, and was stunned that it was Bang On! It lay on top of my front sight like I had spent time doing it. Took it to the range, and Yep, it is right as rain. I liked the three reticles, the auto-on, and auto-brightness features. The optic is large and gives a great field of view, snapping your attention right on target. I couldn't have liked it more unless it was free, but it was worth every penny!