Hero archers who have attained a sufficient level of power may learn how to fletch highly deadly explosive arrows. The art of fletching such projectiles is particularly intricate and time-consuming; it also tends to incur great exhaustion. Because of this fatigue, Archers may find it difficult to fletch many explosive projectiles in quick succession.
Hero archers and fusiliers can learn this skill at sub-lvl 250. There's currently no help file for Explosive Stones but they work the same as the arrows except in slings instead of bows. The exhaustion is one hour of logged on time (although it does not list in the affects command and you are not notified when it is exhausted). It is also important to have config -savespell when getting rid of this invisible exhaust.