HS503CU is a new micro red dot optic equipped with a 65 MOA circle dot
reticle with the option of switching to a 2MOA dot only. Holosun's
highly efficient light emitting diodes and solar panels allow Holosun
solar optics to run without a battery in many lighting conditions.
Additionally, the back-up battery lasts up to 5-years on the dot and up
to 2 years on the circle dot. The "U" signifies a housing design that
shrouds the windage and elevation turrets on two sides.