Sling Mastery (5e Feat)
From D&D Wiki
Purpose: Load ammunition in a sling one-handed; throw items with a sling.
Your mastery of this simple ranged weapon enables you to load ammunition into the sling without requiring a free hand to do so.
Additionally, you may utilize your object interaction to load and fire a small lightweight item from the sling that would typically require throwing by hand. (Vials or acid or holy water, bags of ball bearings, or coins are examples of the types of items that may be used.) Firing an object in this manner will cause the normal bludgeoning damage as sling bullets would, and with normal sling range; but will also carry the effects that throwing such items normally would. (Vials breaking, ball bearings being scattered, etc.)