I have one on every pack I own and that is currently five fullsize packs and one Badlands Monster Fanny Pack. It takes some adjustment and some "practice" to get it just right and I also use a "safety strap" of my own design-very simple as my elderly brain can't cope with complex- and this is the best means of packing a rifle I have ever found.
I have a GunCorral, very well made and super nice people, but, it doesn't do it for me like the K-gunbearer does. I have now used my GBs for seven years and will not be without one. I also have a Safari Sling and several other specialized slings, bleh, the GB beats them all, for me.