John Plaster (The Ultimate Sniper) shares the cleverest real-world account of adjusting fire he’s come upon — from World War II, described in a 1953 article in American Rifleman — in which a spotter put a precision rifleman’s fire on a target that he couldn’t even see:
Using a 20x spotting scope, Robert Sears could discern a German machine gun firing away at 800 yards with such deadly effect that an infantry company could not cross a river.
He had a competitive rifleman comrade fire (using ordinary open sights) at what he called a “reference target” — a rock the rifleman could see, though he could not see the machine gun next.
Observing that bullet impact, Sears announced a sight change to put it closer to the machine gun nest — pay close heed — but had the rifleman fire again at the same rock, which was the only thing he could see that far away.
So, using his powerful 20x optic, Sears twice more adjusted the rifleman’ rounds; then, still aiming at that rock, the rifleman put fire right atop the machine fun position, “either a hit or so close that the machine gunner went down in a foxhole.”
That’s about as slick as it gets.