I have a faint memory of years ago watching a program about a post office shooting where a man grabbed the shooters gun and the webbing og his thumb blocked the hammer. I rember him saying the shooter just kept pulling the trigger and trying to get the gun away. I rember him saying that it hurt like no tomorrow. He finaly did wrench the the gun loose. If I remeber correctly the shooter commited suicide while awaiting trial.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.