I think I will try Andy's idea of a geared motor driving a cam first. Our local electronics store has a cheap motor with variable gears to start the experiment.
If it works then I can connect it to one of "Mr.Action mans" electronic switches.
The 25 mm. Bushmaster gun on the Armidale Patrol Boats can fire at up to 180 rounds per minute but that might be a bit to fast.
It can also be fired one shot at a time which would be much more effective. (for frightening the natives?
) (I sail near a retirement village so I will have to guage the reaction if it is too noisy