Try making runescape gold by smithing cannonballs
The cannonballs are used as ammunition for the Dwarf Cannon and by the Barker Toad familiar. In order to make cannonballs, players must complete the Dwarf Cannon quest as a MEMBER. You are also required having ammo mould, steel bars and level 35 Smithing. The Cannonballs can be created in the furnace with steel bars. You can create 36 cannonballs per inventory. Because of the uses of cannonballs, this can be a great way for making RS gold.
As for the best place to make cannonballs, it is best to make in the Edgeville. To be able to access the furnace in the Edgeville, you must complete the Varrock Tasks. Buy lots of steel bars and other necessary items require for making cannonballs and store them in the bank. Use the steel bars in the furnace to make cannonballs. Once you have lots of cannonballs, start selling them in the Grand Exchange to make runescape gold sell.