Lol,just tried slinging from a mechanical steer(lowest setting)and..well,I now have a fist sized bruise on my right shin
when I finally managed to follow the motions of the apparatus I actually managed to sling two stones(didn´t have a specific target,just wanted to see if I could sling)
my conclusions:
overhand is extremely difficult,and so is the underhand throw.
Got most success when I angled the sling from a helicopter throw.(something between underhand/helicopter)
If anyone of you want to try this use tennis balls.seriously.a sling loaded with a stone at full momentum hitting your shin is unbelievably painful.
I actually thought my leg was broken,but fortunately it was just my pride that got shattered