David needed stones for his sling. From a river bed, he looked for stones that would have been five to eight centimetres in diameter, approximately the size of a tennis ball. Thrown by a skilled slinger, these stones could reach speeds of up to 240 kilometres an hour.1 They could kill and break bones. Slingers were common to most armies at the time (see 2 Kings 3:25; 1 Chronicles 12:2; 2 Chronicles 26:14)2 and able to hit ranged targets with good accuracy (see Judges 20:16).3 Their slings had two long cords with a pocket in the centre. One would shoot by swinging the sling and then releasing one of the cords at the right moment.4
40 Then he took his staff in his hand and chose five smooth stones from the brook and put them in his shepherd’s pouch. His sling was in his hand, and he approached the Philistine.