Your sideways sling release allows you to launch bullets and stones even while prone.
Benefit: While prone, you can use a sling to make ranged attacks.
Normal: Crossbows and firearms are the only ranged weapons that can be used while prone.
Pathfinder Roleplaying Game Ultimate Combat. © 2011, Paizo Publishing, LLC; Authors: Jason Bulmahn, Tim Hitchcock, Colin McComb, Rob McCreary, Jason Nelson, Stephen Radney-MacFarland, Sean K Reynolds, Owen K.C. Stephens, and Russ Taylor.