Caliber:
It’s a little scary seeing so little effect. On the one hand, his gun was too small, on the other, he was carrying it.
Taking action:
I’m afraid that I would probably wait until some innocent person was hurt before taking action. The legal risk is just too great. Shoot before they shoot, and you are shooting skittles eating child. Wait for them to kill an innocent, and you are killing a killer. Sucks.
I'm going to wait until they get me into a position where I'm can't pull my gun without them seeing me, let them herd me and the others into a back room, make us all lie on the floor, then allow myself to be shot in the back of the head. /S
If you could live with the knowledge that an innocent was dead that you might possibly have saved if you acted sooner, then you are hardly the sort of person who others should consult for "advice"...