Treat as a stone thrower in the rulebook with the following exceptions. You may only guess up to 48" for range. Use the cannon misfire table if you roll a misfire and an arrow. However, if you roll a hit and a misfire the rocket hits the ground where you aimed and then shoots off in a random direction before exploding. Roll 4D6" for the distance the rocket moves (in the direction of the arrow on the hit symbol), and resolve the explosion there. It does no damage where it lands originally.