Hi, I'm new! Yeah, that's a hard one to figure out, right? LOL!
I used to be into using the sling when I was a kid, and you guys have me baffled. All these fancy designs, and they do essentially the same thing- huck a projectile a bit further than you can throw them.
When I was a kid, I used a leather patch with a leather cord. No sewing, just tie a tight knot. I could lob a gold ball sized rock accurately about 120 meters. I did a marvelous job of tossing golf balls from our back yard a few houses down and knocking out a window or two. I would have gotten away with it if my grandpa didn't catch me! Yeah, yeah. Dumb things kids do. Funny how we think it's dumb now, but boy we were the smartest people on Earth back then!
Last time I did much of anything was when I was 17 and used shoe laces and a cut up tater sack. Wasn't the greatest, but it did well. I found a good way to hunt ducks or pheasants is to take a hand full of 1" gravel and use it like a shotgun load. Works good if you're within 10-20 meters.