Statistics aside, if someone has a gun pointed at you with finger in the trigger well, you must assume that they have intent to use it. (but it is situational dependent).
If you believe that they intend to use it then no matter what the odds are, you are always better to take some action than no action at all.
A well qualified action that Dave is attempting to develop is even better.
No, I don't believe that you can develop a 100% fool proof method of preventing yourself from getting shot.
I would prefer that the gunman be "connected" and pressed up against me rather than a few feet away...I think this dramatically improves the chance of success if you are a trained martial artist. (again, situational dependent).