Not sure if you watched the video, but the chain they're using is extremely heavy. I would think the projectile would be on the order of one of the single chain links at the end of the small side.
Either way, the weight of the whip is hardly important right, as you are just doing an energy transfer from the falling weight into the small ball, the lighter the whip the better, as long as it doesn't break. If the whip is heavier, it will soak up the energy budget in momentum