Targets/coloring for 600 yards

[FLshooter]

I consider myself fortunate that our club has gotten an electronic scoring system at 600 yard range. But prior to this and when I used to shoot on my friends property we would use 12 inch dirty bird splatter targets if we were not shooting steel.
On a good day with no mirage and decent weather conditions I was able to see 30 cal bullet holes in a splatter target at 400 to 650 yards. A little harder the further you got out there but still doable.We were using my Kowa TSN 822 spotter.