Nulodion's Multicannon Parts is the only place in all of RuneScape that sells the parts of the dwarf multicannon (but only if the player has completed the Dwarf Cannon quest). The store also sells the cannon instruction manual, and ammo moulds to make your own cannonballs. Ammo moulds are used in the Between a Rock... quest. If your cannon decays or you log out while your cannon is set up you can right-click Nulodion and select "Replace-cannon" to retrieve it free of charge.