Your precision with a sling is unmatched.
Prerequisite: Dex 13, Weapon Focus (sling or halfling sling-staff), base attack bonus +3.
Benefit: Whenever you use lead (or metal) sling bullets, you add your Dexterity bonus to your sling damage.
*This feat benefits users of the sling or halfling staff-sling, and is the original concept of Weirdo and Xunal on the Homebrew thread of the Paizo RPG website. (Xunal; Precision Slinging feat)