That distance is even beyond what my rangefinder will register.
Don't feel bad, my is suppose to go to 1200 but I'm lucky to get 450 on the pairee. Don't know what it is.
Anyway I used Mil Dots figuring the average antelope is 15 inches from the top of his back to the bottom of his stomack. So far the number has been pretty close.
I figured 600, only 22 yards off.