I purchased a few 'Tank Guns' from Mato Toys that some of the other Mech Warfare guys have used in the past. These are designed to be used in remote control model tanks which is apparently a popular hobby in some parts of the world.
This gun is much smaller and lighter then the airsoft gun I used on Second Amendment but its firing rate is extremely slow and disappointing. Another competitor at the Mech Warfare 2010 event had modified this same gun for a faster firing rate so I set out to discover the modification myself.
Here is the Tank Gun in all its cheapness glory. It is a slightly different form factor from Mato Toys product image but everything important seems to be the same.
Here I have removed the motor and one side of the gun's casing. We can see the inner workings of the gun. It works almost identical to the spring airsoft gun I used on Second Amendment. This gun uses a much smaller motor with many gear reductions to pull back the gun's spring/plunger.
Here is a picture of the modification I made. Normally the pinion is press fit onto the end of the motors shaft. I simply tapped the pinion down the base of the shaft. By repositioning the pinion like this it is simply bypassing two of the gear train's gear reductions increasing the guns firing rate.
The modification couldn't be simpler and was immediately obvious once I opened up the gun. Any negative long term affects on the motor or gear train is still unknown and requires some testing. Use at your own risk.