The link below is the best gunstrap made in my opinion. Everyone I give them to agrees. They make great presents for landowners that give you permission to hunt on their land, relatives, etc. If you go to the NWTF meeting in Nashville later in February they will have a booth there and you can pick one up. The are made from some type of rubber compound that remains flexible down to 40 below. I have used one for nearly 10 years and it hasn't stretch at all or lost any flexibility whatsoever. They hold the gun tight to you shoulder. They are adjusted to be snug to the gun so the sling doesn't droop and hang down when in the shooting position. You can loop one strap around your neck and carry the gun like a backpack. It stays on your shoulder if you are wearing a backpack. Easy to adjust. Simply the best there is in my opinion.
Video of the Slogan gunsling
http://www.plaza-paquette.ca/webaltraflex.wmv
Website
http://www.sloganoutdoors.com/
Mouthcaller