Could this one be as simple as it sounds? If he’s thinking about the odds, it would be 1 out 3 for the first trigger pull versus 1 out of 6 for the second. But he saw] something, so he’s got good vision.
He saw 2 bullets at the lower end of the cylinder. Pulling the trigger one more time would not allow either bullet to get into the chamber.
Correctish, but phrasing could use improvement. He could have seen only one bullet. In fact, if he had seen two, the upper one of those two would have been the one that killed him, because pulling back the hammer (as you are required to do on a Colt .45, specified in the Puzzler) advances the cylinder by one chamber and would put that chamber and its round, if any, under the hammer.
Remember it’s a six-shooter. From a front view, there are only four chambers visible, two on each side.
Still, pretty good vision at 40 - 60 feet.
One the first shot…when the hammer was pulled back…he saw 2 bullets rotating away from the chamber. That will work.
Hard to call that “the lower end of the cylinder” but still a good point. Remember it was never specified that the rounds were loaded in adjacent chambers.