They should try it with an airsoft gun with a bb in it.
Then we can see if he can grab the gun before he gets popped in the head.
that wouldn't be the best way, as a real criminal might expect or not expect for the person to react, along with the fact some criminals are hesitant to pull the trigger on a gun. with a person using a bb gun, they won't hesitate because it doesn't kill and they know he will take the gun