My favorite is a sling I make from some kind of green, military surplus, carry strap. I'ts about 2 inches wide, and made of some kind of cotton canvas. I take the hooks off of each end and replace them with a quick detachable swivel. It doesn't slip on my shoulder, really spreads the load, it's easy to adjust and is very light weight. The last ones I bought were about $3.50 each.
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Harry