From Guild Wars 2 Wiki
Hold down the button to increase the range at which the catapult shot travels, and release the button to fire. Fire gravel to damage players and siege.
— In-game description [?]
- Range depends on how long the skill is charged for, and also on the catapult's elevation; placing it higher up will increase its range.
- This skill becomes Fire Boulder when Load Boulder is activated.
- This skill is replaced by other versions for players with ranks in Catapult Mastery.