Slings are mucho fun, and definately not worth buying. The ones I made were just shy of fingertip to fingertip length, with paracord strings and leather pouch.
I put a fixed loop at the end of one string, and typically put it over my first two fingers. The other line went under my last two fingers and over the first two, pinched against the index finger with my thumb, I open my thumb and last two fingers, stone flies. I use a whirling-type throw, swing it around a couple times, and let loose. You can get absolutely _amazing_ distance and power, but I was never successful enough at accuracy to hit something animal size reliably, but I could launch an egg-sized rock 200 meters with enough force it would shatter (like lots of little-bitty pieces, not just crack) upon hitting a concrete wall.
I did try 'grapeshot' once or twice, with marble-size stones. Range was very short, but I think I could expect to actually kill small game in that manner. It is how I would hunt were I surviving with a sling, though I prefer snares to hunting any day.
Stryver