Ah... Another martial arts thread!
It seems that there are two major questions in this thread: 1. What happens when a trained martial artist is confronted by a guy with a gun? and 2. Does anybody have any cool stories about empty hand vs. gun?
As to the first question: After a few years of training and testing on this topic, it has been my experience that, around 99 times out of 100, when a trained martial artist is attacked with a handgun at close range with no prior warning, the guy with the gun shoots the martial artist before the martial artist can figure out what's happening and take the gun away. That other 1 time out of 100, the martial artist grabs the gun away before he can be shot.
My qualification to these findings are: The guy with the gun typically only gets one shot off before the martial artist is on him, and that one shot is typically not very well aimed. So, the martial artist usually suffers a non-lethal wound, and manages to get the gun away.
As to the second question: The only story I know about is a parable on proper practice. You must remember the statement, "You will perform what you practice." Make it your mantra, and live by it.
My martial arts instructor, in his younger years, was an army man. He would train with his friends on the base in empty hand weapons-disarming techniques. Each time they would run a disarming drill, he would grapple the weapon away from his training partner, and then he would calmly hand the weapon back to his training partner to repeat the drill.
One night, my instructor was in a parking lot on the base, and he was held up by a mugger. The mugger drew a weapon and demanded my instructor's wallet and car keys. My instructor, without thought or hesitation, clapped his hands down on the weapon, stripped it from the attacker's hands, and then calmly handed the weapon back to his attacker! The attacker took the weapon, and my instructor repeated this process three more times!!! Each time, he would strip the weapon, and then calmly hand it back to the attacker! He finally woke up and realized what he had been doing, whereupon he took the weapon away for the last time and kept it. The attacker was LITERALLY speechless by the end of the exchange.
Moral of the story: Practice like it's real. Because, when it IS real, you will perform what you have practiced!