The elcan c79 optical sight was designed for the C9 lmg and then adopted on the C7A1 with the flat topped upper receiver. It is adjustable for range from 200-800m with 5.56mm ballistics. It has a 3.4x magnification and the objective lens is 28mm, uses a tritium illuminated reticle and has an eye relief of 70mm.
It’s a good fighting sight. The mil marks inside allow range estimation. The ones we use are very beat up, with the battle sights on top mostly worn off. It does its purpose which is to allow the combat arms to engage targets day and night out to the maximum effective range of the rifle / lmg. There are much better optical and holographic sights for short and long range work.