Adding few more info-help using siege weapons to destroy walls or enemy weapons:
- Only 1 shot from catapult or trebuchet to another trebuchet (enemy) is enough to destroy it, if you hit it properly ofc, and if fails maybe because lag, or because you need little bit more precission aiming it (use B key for better/slower aim, as @Lenna said above)
- Not all walls can be destroyed in all maps, this depends of what was the idea of author, and how much walls he enabled to be destroyed, and at same time, not all walls have same hp value. As a standard or default, central/frontal builds/walls like gate have higher hp, and all at sides are decreasing in hp, proportionally to distance of gate (more far from gate = more weak)
- Finally, add to this that I said above: lag sometimes causes that shots fails, so maybe you need more hits to destroy a same wall, in diferent ocassions that you can play that same map.
understand better now?