Michigan Scott was on target telling you the canvas Garand sling. It works well and is cheap. After you learn how to shoot with it, then you will know what you do and don't like if you shop for a more expensive one. I use them on my bolt guns at the range, and carry one in my pack while hunting. What I like about them is the loop around you upper arm doesn't change size by the keeper slipping. What I don't like is the lack of quickly repeatable adjustments.
