I wonder what kind of energy a 44 flat nose handgun bullet out of a 44 magnum revolver has left at 600 yards..or even 400 yards....are you sure it was the right distance??
There are three factors that determine bullet effectiveness; velocity, bullet weight and bullet diameter.
Velocity comes and goes, but the nice thing about a big, heavy bullet is that even at long range and low speeds it's still big and heavy.
Energy, shmenergy a 240 grain 44 caliber bullet is a force to be reckoned with.
Again, please note that Keith did not attempt this as the first shot, he was shooting a wounded animal, so different ethical standards applied. He emptied his revolver at the animal and his skill and a good bit of luck saw him through on this particular occasion.