This is somewhat off topic, but I recently saw a demonstration of a staff-sling (a weapon that was believed to be prominent in the ancient Near East at one time. The operator of it could hurl surprisingly heavy stones out to distances just shy of longbow range...and do it consistently. The only downside is that it required noticeably more room to operate than a bow. Another potential drawback was that it delivered concussive force instead of piercing-type damage. Still, I was amazed at the dents that it put in sheet-metal plates at distances of around 80 yards. Getting hit with one of those stones in a relatively unarmored spot would definitely ruin your day.
Slings were powerful but I think shields made them obsolete. A wicker shield might not be enough but a hide shield or hide and wood combined is going to negate that weapon and make something like a javelin more effective even if it has shorter range.