Cannonball method versus fax to bow string method?

I have over 3m in the game Runescape and i want to increase that. Two methods i have learned to make money with money are making cannonballs out of steel bars that i bought and selling them and another is buying large contitys of flax and spinning them into bow strings i want to know which is better pay out for less work and which is faster and buy how much. I would really apreciate statistics. Also if you need to post another way to make money you (you wont get best answer)