Many years I carried heavy magnums. Now I live in the land of the lilliputian blacktail.
Anyways, never found any system or sling that worked. Five km in, I was ready to throw away my rifle and walk out. Then I discovered what worked for me. Crossed over my back, barrel behind my left ear. I cut the web just above the bottom quick connect swivel and install a backpack quick snap....juice box thingy.
So across my back, reach down and grab the tag end of the strap, pull it tight. Never moves see a animal, snap the quick connect and the rifle swings around, right into my arms. But a minute to loosen it, reconnect, sling it, tighten it down. Works for me, no fatigue, no sore/switching shoulders, no losing the rifle to the Alder monster, hands free.......