It's kind of like the Billy Dixon shot. Dixon borrowed a 50-90 Sharps as he felt his 45-90 would not reach, he fired at a group of Indians and on his third shot, he knocked an Indian off of his horse at nearly a mile away. The US Army verified the distance at 1538 yds or 7/8 mile. The question is, was he aiming at a particular Indian or, was he aiming at a group of Indians and just happened to hit one? I tend to believe the latter. Doesn't say if he used cross sticks or off hand.
Regarding the Quigly shot, before his first shot he is taking his time on aiming but when he is interrupted, he then shoots before he can line up the sights on the target. But, we have to keep in mind, it's Hollywood, where miracles happen.