Hmm.... another unpickable lock thread
But anyway- if I read your plan correctly, gravity has no effect on the pins, no? Well, lets say you have 5 pins and the cuts are 5,3,4,2,1. When you insert the key, the first position that enters the keyway (position 5, depth 1) will "unscrew" the pin very high, but when you finish putting the key in nothing will be able to force it back down to fit the first position (depth 5).
And plus- there is no such thing as a 100% unpickable mechanicle lock. You can always manipulate it to simulate the key.