Stand-out mechanically simple Shooting mechanism

[Anirchy]

Many of the teams I've seen on this forum are using things such as catapults and slingshots, but I'm pondering a pretty feasible way to incorporate a more responsive and consistent firing tool.

This idea is quite similar to popular Airsoft-Gun gearboxes. Here is an example of the latter: http://www.airsplat.com/Images/gearbox.jpg

Now the idea is practically the same. A motor moves high torque gears to pull back an object (threaded on the bottom to mesh with gears) against a spring and are then let loose to push the object forward. In the airsoft case it would be a cylinder creating mechanically conceived High Pressure Air, but on the robot the object would impact the "boulder" directly and propel it outside the barrel.

I'd like to know your thoughts and if you have any ideas on shooting mechanisms please post in this thread.