Algodoo

This cannon shoots small but very dense bricks at high speed and accuracy.

My first upload, so I`m not sure what sort of bugs might reduce its performance for you, but it hardly ever fails for me and can shoot pretty rapidly. All eight of its rounds can be put in the air at once.
Arrow keys to move. A and D aim. W shoots and if the swinging arm gets stuck S will unstick it.
Zoom way out to find a brick wall. The cannon should be able to hit the same part of it consistently and tear it down in five shots or less.

It also shoots backwards and upside down, but not as well.