Converting a modern centerfire revolver to full auto? Well, do you recall how the Australians modified their SMLE to become semi-auto? The put a gas port on the barrel and the gas operated the op-rod that rotated the bolt. I suppose the same could be rigged up to push the hammer back to full auto. If the trigger is kept depressed, then the hammer would automatically fall as the op rod disengages it. Then it'll be a matter of dexterity to see if you can get only a single shot off or a burst.
But, if you want to do it a very old fashion way, seal five of the six nipples on a cap 'n ball revolver. Bore a hole from each cylinder such that a spark would transmit from one to another. You may have to drill through the cylinder and then weld up and turn on a lathe to clean up your mess. The Cap n' Ball will then function like the English Nock Volley Gun made famous again in the Sharpe's Rifle Series. BTW, if you want to see a genuine early model of the Nock Volley Gun, head over to the Charleston City Museum in SC.