The Qin army only possessed 24 catapults but their accuracy surpassed that of the 100 catapults set up by winged skull. The catapults in the city were clustered so after two rounds of both sides heaving rocks at each other, Qin has already lost half of their catapults while 52 of those in the city were destroyed.
Fortunately, the catapults in the city were made of bones and not of metal components so when they were crushed, there were no wooden shards flying around.
The bone catapults that had been crushed became a dismantled pile of components. Only those soldiers that were hit by the rocks directly were unfortunately killed.