I know that verse well. (The Second Epistle of Pistols Chapter 9 verse 99.)
(Scholars debate to this day whether or not David could load that sling with more than one stone at a time!)
https://www.biblicalwarfare.com/sling-weapon-in-ancient-warfare/
"A slinger would place a rock or other similar projectile in the pouch and pull the cords taught. The warrior would then spin the sling until he built enough momentum to release the missile. These missiles could travel up to 62 miles per hour (100 km per hour) and reach 1300 feet (400 meters) based on estimates.1 That would give a sling an advantage over the bow and arrow. Although making a sling and finding the missiles was rather easy, learning to use one effectively required extensive training and practice.
Expert sling throwers were incredibly accurate and could cause real damage when the projectile reached its target. The stone missile could cause blunt force trauma shattering bone and damaging organs, and could hit an opponent with sufficient force to kill him.
Hannibal Barca, one of the greatest commanders in military history, successfully used slingers against the Romans. In the Battle of Cannae in 216 BC, a Balearic slinger, one of the 2000 slingers employed by Hannibal, hit his mark. The Roman general Lucius Aemilius Paullus received a mortal wound from the sling missile. 2 He was one of over 55,000 Roman casualties during that battle. The Battle of Cannae was a disastrous defeat for the Romans and a testament to the effectiveness of slings in battle."