Greetings @LJPRMC,
I think we tend to over complicate things. I had just this need before I shot my first 600 yard shoot last year. I had the chronographed velocity for my load so just ran the trajectory using the Hornady on line software in 25 metre steps out to 600 metres, 600 yards is very close to 550 metres. Next I made a tall target with a NZDA 100 metre target taped on the bottom and the predicted 200 metre POI marked on it. The rifle was zeroed aiming at the bottom target with the shots falling on the upper mark. This was done on my home 200 metre range. The first shot at 600 yards was a 4 and the Target software validated my predicted velocity at that range.
I find the fascination with zeroing rifles at 100 yards or metres hard to understand. For bush hobbits this is likely fine but for rifles that will be used at longer ranges surely 200 metres would be a better option. My hunting rifles (regrettably hunting in name only these days) are zeroed at 200 metres or whatever range the MRT is 50mm or less. I see that your most often used range runs from 90 metres to a max of just over 350 metres. A base zero at 200 metres would extend your just shoot range considerably for a rifle in the 7mm Rem Mag class.
Regards Grandpamac.
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