Originally the cannonball myth was scheduled to air the previous season. Unfortunately, during taping a cannonball hit a house and the segment had to be postponed until a thorough investigation could be made and until a more remote location could be used. When the Build Team resumed the experiment everything went off without a hitch.
Grant excitedly mentions that their experiment is likely the first time in 400 years that somebody has fired a cannonball made of stone. However, in season one, episode nine of Mythbusters, "Lightning Strikes Tongue Piercing/Tree Cannon/Beat the Breath Test" (2003), Jamie fashions a cannonball out of stone, which is then successfully fired from a cannon made out of a large tree trunk. Moreover, unlike the cannonballs created in this episode, Jamie's original stone cannonball was made using only era-specific hand tools and chisels; no modem power tools were used.