I've had the best luck on seeing bullet holes at long range with light brown butcher paper. Even then its hard to go out too far beyond 600 yards and see anything. Generally its the mirrage that kills the visibility.
I have, however, been successful using a 4-22X US Optics rifle scope and could easily see 7mm Berger 180 bullet holes from 1K when shooting on a 12"x18" black shoot-N-see. Granted the mirrage was negligible that day, but the holes were obvious to see, even just using the rifle scope. With a soptter it would have been easier still.
Similar result with good hit visibility when shooting a freshly painted (white) ARmor plate steel target at 1,350 yards. Hits were easily visible with the same rifle scope, until the marks were overlapping on the target. Even then, the "gong" gave me all the feedback that I needed.
JeffVN