A cluster weapon is a form of grenade launcher that can fire a single grenade or (if loaded with appropriate grenades) can expend two identical grenades as a single attack. In the latter case, the grenades act as a single grenade of the same type (with a single attack roll, dealing damage only once, and so on), except its radius is increased by the listed amount listed and the save DC of any effects created by the grenade is calculated using the cluster weapon’s item level if it is higher than the grenade’s item level. Attempting to fire two nonidentical grenades results in an error code and the weapon does not fire.