It's no different than any other hunting -

Know your quarry, know the limitations of your equipment AND know your personal limitations BEFORE the shot presents itself.

Hot Core,

Heck I have acquaintances that can do the same thing at 100 yds!! But to hear them tell the stories they are tremendous LR shooters.
Disturbing story....to lose such a big bull! I'd lose some sleep over that one.

FN in MT

LONG RANGE shooting is the same as anything, practise, practise, practise.
The last time I got to shoot on a military electronic popup range they had miltargets out to 900 meters. At 900 meters I went 20 for 20 with the exact same rifle and bullet load I hunt caribou with.
I have a 100 yard range in my back yard and I have several spots out in the state forest where I can get out to 800 yards. THere is another I just found that I am willing to bet is over 1200 yards but I haven't set up the lazer yet to find out.
When you can regularly shoot 7" groups at 800 yards, shooting at a caribou at 400-500yds with the same gear is not that tough a target. I took the first 2 this year at over 400 yds and because of the snow couldn't get a good rest so I dropped to my knees/sitting in the 3 feet of snow and crawled into the sling and took them from essentially an offhand position. With the Shepherd scope it was a dead on hold, all I had to do was keep the X on the target.
It is not something just anyone can do, but with the right gear and practise, it's just another hunting shot.