Zero Shift from day to day

[gunsandgunsmithing]

I am no math hguy, and certainly not a gunsmith or even a scientist. But I do know this.

When shooting a certain farm (any summer weather over 75 degrees and full sun) in NY, out to 600 yards, my rule was:
9AM-Noon, use normal zero and click calulations on chart.
Noon...down three clicks from the chart
1 PM...down four to five clicks
2PM down 6 clicks
3PM down 3-4 clicks
4PM down 2 clicks
5PM and after, use regular zero.

It's the sun

Sweet but a cloud can pass over at any time

 

[calgarycanada]

Shoot a 20 shot group and use centre of that group as zero.

 

[alintx]

Ammo heating up can cause this easily. Didn't know your temp change, but could be the culprit. Try loading with a different powder and repeat the tests

 

[snert]

Sweet but a cloud can pass over at any time

Then wait a minute