The barrel bomb is created when putting a pot of quicklime and ground sulphur on a barrel of naphtha during the Regicide quest. After obtaining the Barrel bomb, a strip of cloth needs to be added to activate it. The bomb is then to be shot at King Tyras, killing him in a fiery inferno.
This is one of the heaviest objects in the game, weighing 32 kg. Other objects that weigh this much include the Barrel of coal-tar, Barrel of naphtha and Naphtha mix used to make the bomb in Regicide.