Laser range finders and PDA ballistic calculators could make the job a lot easier, but how do you account for wind over such a long distance?
That’s where the skill comes in. You can use a Kestrel wind meter where you are, but over such a long range, all you can do is read the wind from effects on grass, trees, smoke/dust, etc and make an educated guess. You then enter the info into your ballistics computer and it spits out a wind correction.
TFA stated that the wind was dead calm, but over a range like that, it would take some extraordinary luck for it to be dead calm over the whole path of the bullet.