Sig550 with 4x optic from 1976. QD mount allows true return to zero. The scopes are slowly getting phased out as the supply of parts runs out.
The thin bipod is surprisingly sturdy and allows good control of automatic fire. It can be removed very quickly without tools. Fire selector is Safe-1-3-30 but the slow rate of fire makes 3 unnecessary. The trigger and the sights are very good. The fire selector lever is too short for most people and the rifle has to be turned to the side for it to be reached easily.
Reliability in the dozen rifles I’ve seen used (including mine) was 100% over a full-day course in all kinds of weather. I literally did not see a single stoppage of any kind over 300+ rounds per person. In my opinion, this rifle is superior in handling and operation to both M16/AR15 and to the US-made Sig556.