This list is long, several long winters setting by the fire reading long.
My most dog eared would be Hatcher's Notebook. And its companion piece, Machine Guns 1917. Don't let the title fool you, in those days long range shooting was the name of the game.
The best by far, (though a bit advanced) is James McCoy, Modern Exterior Ballistics. Brush up on your math for this one.
And of course I have most if not all of Brian Litz' books.
Don't neglect the older authors, Ingalls' ballistic tables Paperback – January 1, 1918, is a good one, or Ingall's other writings. Or Dr. Francis Mann, (th Mann devices are still used by the Army today.
At the turn of the 19-20th century extreme long range marksmanship was the name of the military shooting game. Don't neglect the old Marksmanship/Training manuals of the period.
This is just a short list, I have several more taking up a whole wall in my man cave. It just depends on how deep you want to get.