We all know the state of pvp, so, why not have a light infantry kind of weapon, a ranged one that you can shot on the move while chasing or being chased with swords, axes and spears being left in the state they are now.
Add a move "shot" that works only with slings and lets you throw stones on the go, lock it behide the hunter credo or rage, it might put one of the most early and unseen weapons into use by dedicated 'light infantry' used to chase down wounded enemies, or as a side arm for every warrior.
Also add cast bullets for slings, basically every civilization who used slings in war at some point made cast bullets or stone carved ones, it takes a nugget, or makes 10 from a bar of metal or something.