There are many techniques for disarming. If you are serious about learning how to disarm someone, I suggest that you study several of these systems and become proficient in them before trying to design your own.
The instructors that taught me disarming techniques said that trying to disarm someone who is pointing a gun at you is one step short of suicide.
Finally, your "method" assumes that your single strike will instantly render your attacker senseless for some period of time. That just isn't going to happen 99 times out of 100, even if you are Chuck Liddell. And you're not.
If you are trying to disarm someone, go for the gun. You must know your technique cold. You must choose the correct technique. You must apply it quickly, decisively, and with surprise. And even then, you may well get shot.
With your technique, you'd simply get shot.