Well I know this is rather late but I have an idea...
I would like to call it the Acorn Sling, a sling for lightweight projectiles. My thinking is making a sling with a good cupped pouch, kindoff apache style, and sewing in a little weight. Simply put, a weighted pouch to make the sling easier to control with lightweight projectiles.
Sadly I'm very busy currently with matric and other work etc so I can't make it currently but I would love to experiment in the near future.
And if you want feel free to experiment with this idea.