Re: Calculating zero shift in different conditions?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TargetTerror</div><div class="ubbcode-body">I am familiar with how to use the ballistic calculators, and have used JBM's online calculator extensively to good effect. One question I have is how to calculate the zero shift for a given load when the atmospheric conditions change. Ie, say I zero my rifle at 200 yards in 95 degree heat, with a given humidity and pressure (so at density altitude X, if I understand things correctly). If I change nothing on my rifle and shoot the same ammo at 200 yards when it is 30 degrees out (or otherwise a different density altitude Y), the POI is likely to shift since the air mass the bullet travels through is different.
Ballistic calculators seem to be limited strictly to calculating trajectory when a bullet is <span style="font-style: italic">zeroed for any given density altitude</span>. Is there anyway to calculate the zero shift for shooting the same zero in different density altitudes? </div></div>
Most applications that have the ability to enter "zero conditions" and "Field Conditions" are suppose to calculate the difference properly. Understanding that as the temperature changes more likely BP and humidity will also change, but for the purpose of this example I'll only change the temperature leaving everything else the same.
I'm a ColdBore 1.0 user and in this program I enter all the conditions for my zero and as I travel and the weather changes I enter my new conditions in the "Environment Conditions - Field" and the application tells me what adjustments I need taking in account the Zero conditions and the new Conditions.
Let's start by entering all data and conditions for Zero.
<span style="font-weight: bold">Note: Field conditions are off</span>
<span style="font-weight: bold">Field conditions are off</span>
For comparison purposes I entered the zero conditions only and saved this data to "Track 1"; then with the original data on "Track 1", I recalled it on "Track 2", turned ON the Field Conditions and entered the new info.
<span style="font-weight: bold">Note: Field Conditions are on</span>
Now I run the two Tracks side by side so that the results can be compared up to 1500 yards.
<span style="font-weight: bold">Note: Track 1 and Track 2 are first compared in inches and then in MOA.</span>
As others have said, the difference is too small to be noticed at 200 yards, only 0.1", but as we shoot farther away we need to care more and more.
At 900 yd, the difference will cause a complete miss on a mule deer.