Scattershot

Load rocks when you want to hit people, not walls. A volley of heavy stones lands in a wide pattern, which is exactly what you need against defenders on a roof, a wall walkway or a crowd at the gate.

It is also the cheap shot. Made from stones, it costs next to nothing, so a catapult crew can spend it freely while the propane bombs that took real effort to build wait for the moment that matters.

Against stone and metal it does next to nothing, so don't bring a box of it expecting to break in. Even wooden walls soak up a huge number of volleys; only twig gives way quickly.

A siege usually ends up mixing three rounds: rocks to keep heads down, firebombs to spread flames where defenders gather, propane for the actual breach. If nobody on the other side is shooting back, you don't need the rocks at all.