I saw that episode too, and I beleived somone posted the video clip on here, we mocked the poor imitaion of slingers they used, and then went on to other discussion.
I beleive they showed the one piece leather sling, showed them slinging somkind of weak underhand at a sheild 30yards away, and then showed a few of a few stones hitting a sheild.
I believe CA's comment was "If those stones that hit the sheild came from those slings, I'll eat them"
You could probably find the thread if you looked around a little.
The sling was pretty prevelent in almost any army without a lot of funding due to it's extremely affordable aspect plus it's incredible performance.