Could be cool to see utility ammunition for slings instead of going the route of another RT/repeater/dual load etc.

They could be LT as well but using a sling increases accuracy and maybe potency. They wouldn't do direct damage, generally.

These could be one time use and crafted through alchemy and/or engineering.

Some quick ideas

sticky balls - stick to your enemy, causing random roundtimes and/or hiding penalty. Tend to remove
stinky balls - causes an unpleasant odor that makes your enemies keel over and gag
web ball - expands into a web that keeps your enemy in its current position (lying down, kneeling etc., missile, melee etc)
paint balls - temporarily blinds enemy, or reduces accuracy perception if succesfully hits the face.
smokey acid balls - explodes on hit into a gas that enemy inhales for nerve damage, but no HP damage

buckshot - this would be a damage AOE, less accurate