I would have to have more information about the exact setup of your robot, but with the word " hit" i would assume you are running something that is spinning. If it is spinning, I would best solution is to remove the gearbox. Run the motor to the weapon using a pulley on the weapon motor and one on the weapon. You can change the sizes of the pulleys to adjust the ratio of the weapon speed.
I say I need more info because you may have some awesome new weapon that would benefit from this set up that I have never seen.
If you are not breaking stuff then you are not learning......