Usually around that 600 yard range will be where you start seeing things start to go of the rails if your not quite right.
You gotta nail your enviromentals first, you then need to give your calculator good data, shooting chrony's will leave your some room for tweeking so make sure everything else is nailed. Scope hight, range to target, BC, turret value, then you can concentrate one basically zero and velocity.
It's easiest to verify your zero is solid by shooting at 300 on paper, if your zero is of a little it'll show because velocity or BC isn't really visible yet so I tune my zero hight to match what it should be.
Then put up paper at, 300, 600 and 1000 and I dial and shoot these fast one round at each as close to the same condition as possible.
Measure it up and tune your velocity, I can usually get a solid tune to 1500 yards inside 20 rounds with this method.