Sling Expertise

Benefit: You gain a +1 feat bonus to weapon attack rolls that you make with a sling. This bonus increases to +2 at 11th level and +3 at 21st level.
    In addition, when you make a ranged or an area attack with a sling, you don't provoke opportunity attacks for doing so.

Published in Heroes of the Fallen Lands, page(s) 317, Heroes of the Forgotten Kingdoms, page(s) 318.