HS515BU is a red dot sight that features the circle dot reticle with the option of switching to a 2MOA dot only. :B signifies that the battery is in an internal tray, accessed through the side of the optic with a removable tray. :U signifies a housing design that shrouds :the windage and elevation turrets on two sides. Employing new LED technology, :the life time for one :CR2032 battery can reach :2 :years :if left on constantly. However, :the motion based automatic on and off feature extends :the battery life dramatically beyond that for the average shooter. :Includes flip-up lens covers, a kill flash filter and a quick release mount.FeaturesMotion based automatic on &: offParallax free with unlimited eye relief.Switch between circle dot and red dot reticles.Kill flash included.Battery tray.Flip-up lens covers won’t obstruct your vision.13 Co-witness QR mount includedQuick release mount. Adaptable to Picatinny or Weaver rails.CNC machining with T6061-T6 aluminum housing.