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Looking for some help with this one:
If I zero a rifle at 200 yards at sea level at 15 degrees Celsius and then for arguments sake go on a trip to 1000m altitude at 5 degrees, how do I get the right data for this change.
I have been using the JBM website trajectory program but if I change the altitude or temperature, it still considers the zero to be 200 yards. Which I assume it won't be?
Can anyone offer any advice on this? Would be much appreciated.
zero at 100y then any atmospheric changes will have a very negligible difference.
The best ballistic calculators like AB you can put in your zero atmosphere if you want to zero past 100.
At 200 you can use it but still not huge if your only shooting medium range.
If putting atmospheric factors in you will need the likes of a kestrel 2500
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Run it with the zero at 25 or 50m for each altitude/temp combo and compare the predicted drop at 200 maybe? Difference in drop should be close to change in impact. Using a 25m zero should put it close at 200m anyway so trajectory calculations should be close to those using a 200m zero but won't change much when program tries to keep zero.
differences will be tiny & no real world consequence at least out to 500 yards or so.
Thanks for the fast response guys.
the biggest issue at height will be oddball winds due to pockets of warm/cold air and turbulent wind but at normal shooting distances its not an issue. i find the best thing to do if time is available is scope upward to the animal and look at the foliage to gauge wind across the distance
I had a play with the Strelok app and it does exactly what you are trying to do!
You can set the altitude, temp and pressure for when you zeroed the rifle, and do the same for where you are shooting now. It doesn't try to keep you zeroed like the program you are using.
For my 243 load using your altitudes and temps, it predicts 0.3cm low at 200m (yes that's 3mm low, 0.05 MOA, so not much change at all.)
308 firing 178gr eld-x it predicts 0.7cm low at 200m, still only half of a quarter MOA click.