Shooting 450 yards is quite easy with the right set up, lots of practice and a laser range finder. I live on Vancouver Island and routinely take black bears at 300+ yards.
You need an accurate rifle like a Remington Sendero, in a powerful flat shooting caliber. You need a very solid rest, and ya better be shooting a load that will group 1" at 100 yards. Then you need to actually shoot and practice at those ranges to see what your actual ( not from a book) bullet drops are.
The best practice for long range shooting is setting up the plastic 4L milk jugs full of water at various long ranges, and then hit em!(please take them with you after your done!)
As for a .243 on Elk at 450 yards, he could quite possibly have hit the animal at that range, but certainly not with enough energy to anchor an animal that size properly. I consider the fast 7mm's the minimum for long range shooting of deer, bears, or elk.