Armor Penetration and Armor resistance.

[Paullus Scipio]

Thank you Wolfgang !
In the words of a popular T.V. program....."Myth Busted" !!!
As that program also showed, the Hollywood myth that powerful guns knock people off their feet is just that - a myth.
So, no 'superweapon' slings then.
It would appear that greek slingers of the Hoplite era were concerned less with 'armour piercing' than with range.
Several greek "glandes" made of lead are of the order of 50g, and some are known as light as 24g, and if we allow a range of around 250-300m for the latter, they have a kinetic energy of around 30-36 joules, which is around the same kinetic energy as the Asiatic bows they opposed.
Xenophon mentions that the Rhodian slingers ( using lead bullets) could outrange Persian ones ( presumably slinging stones, but maybe not ) and"further even than most of their archers" (Xenophon, Anabasis, 3,iv )

That slings, arrows and javelins were similar in effect, range, and performance is shown by the fact that all three were used throughout the greek and roman world, and it is not until both Asiatic and Western bows get more powerful in mediaeval times, that slings and javelins are displaced as missile weapons.