I like the 7/8" one piece leather slings of yesteryear...I don't use a sling but I always carry on in my jacket or day pack just in case the need arises such as fatigue, but that is seldom, and for a belly crawl its handy..

I do make my own canvas (webbing) slings for my binoculars that I carry in the African carry over my right shoulder and on my left hip just above the belt and I can slide the binoc to any position I want such as on my chest and the canvas sling will hold them there all day long....