HDx - Mid Sized Red Dot Sight With the rise of the PCC competitions, there was a need for an overbuilt mid-sized red dot sight with modular mounting options. It had to be fast, durable, and easy to use. Featuring the new M5 Reticle, the HDx is fast and nimble, up to 30% faster than a conventional dot. The auto brightness controls which are brought over from the success of the HD7, the HDx is sure to be a favorite, as the optic can age the reticle brightness dynamically. With modular mounting the HDx will be at home on a Picatinny rail, no matter if it is a AR-15 platform or something from the Eastern Block. The power source could not be easier to find or change. positioned out of the way in the 2 OClock Position, we use a common AAA power cell to light up the reflex sight. NOTE: For the best long term power solution we highly recommend a quality lithium battery for use in the HDx.