Projectiles have historically been stone, clay, or metal, but any thing may be thrown from a sling. It is possible to throw more than one projectile at a time from one sling, but the accuracy is greatly reduced. Assuming that we throw one thing, it shouldn't be larger than the width of the pouch from which it is thrown. Slings will throw stones, oranges, eggs -- you name it! It might even throw paintball grenades. The weight of the projectile may vary up to a pound. Distance, however, is reduced as the weight goes up. In the future I plan to offer stats on the best type of projectile to use, so check back.