i use a standard 1" or 1 1/4" nylon sling. it's called a a super sling, and made by outdoor connection. it adjusts very easily, adjusts short enough to wrap over your left elbow for a offhand shooting aid, and comes in a few different camo colors.
encore- i install a sling stud out in the tip of the walnut forend, and another into the walnut grip. needs to be carefully drilled to prevent splitting.
contender- i install a machine threaded sling stud as replacement for the front forearm attachment screw, and another wood screw type into the walnut grip.
the one contender i have with pachmayers, has a long stud for grip bolt relacement, but was already installed when i got it. i replaced the single forearm attachment screw with a machine threaded sling stud.