Hey Arturo. I have made three slingshots so far. two as gifts and one for myself. Unfortunately I broke my own by shooting a much much much too heavy lead ball <img src="http://illiweb.com/fa/i/smiles/icon_cry.gif" alt="Crying or Very sad" longdesc="11"> but they were all rigged with two bands per side TB gold cut to dimensions i obtained using Joergs Calculator. I only wish I had put three per side for more power. Right now I dont have any hard wood to build slingshots from so i just draw up blueprints <img src="http://illiweb.com/fa/i/smiles/icon_smile.gif" alt="Smile" longdesc="2">