Quoted from metallik:The physics are wrong. Once you reduce the size of the pinball, it doesn't weigh enough, it'll fly around the playfield unless the flippers are super weak, it won't trigger scoring elements properly... shit just won't work right. Safecracker is about as small as you can get and still keep that proper feel.
Could fill the pin with liquid to get the speed right. I'm thinking of those toys where there are no electronics and you just launch balls around. Definitely would be re-inventing the wheel.