You know it's pretty easy. Just set the cannon at the height you prefer, I got mine on 31. Then just hold space. This way it will shoot at near maximum speed and when the shot is over, it automatically starts the next shot.
Just use something to keep the spacebar down and leave it on a night... That's how I imagine those people that got 4000 to have done it...
In south africa some dogs were killed by angry villagers. The dogs have had sex with a 12 year old girl in the village. The other villagers grew suspicious of the matter and decided to keep an eye on her. So then they caught her in the act with 3 dogs. The villagers went crazy and killed the dogs...