Why is the guy using a .45 cal. smokepole and not a .50?

I probably wouldn't take the shot with a .45 cal., if it was a .50, I would probably shoot him at the base of the neck, but a shot to the vitals would go through and richochet on the water, sending it pretty far.

Considering your scenario, I wouldn't take the shot, I'd probably wait for him to move to a better spot.