Has anyone ever recorded a target at long range on a sunny/cloudy day to see how much a center of a target will move?
A Leaphart
A Leaphart
Recording Sunlight at 600 to 1000 Yards
- Thread starter AWLEAPHART
- Start date
I know mirage will have target displacement but I was reading some about light alone. Setting up zero on a cloudy day at 600. Then back to the same range/distance on a bright sunny day will make you shoot low?. (If I'm understand what I read correct.)
A Leaphart
A Leaphart
Jay Christopherson
Not An Admin
I have had a .5 MOA shift in zero (requiring less turret elevation) from first match to the third match on a hot sunny day at 600yds. When I first noticed this when wet behind the ears I thought my load was picking up a bit of velocity but a later match shot alongside a Labradar said otherwise. It was then that I realized how much mirage was raising the apparent image of the target and I was unknowingly raising my front rest elevation to put that 'raised' image in the crosshairs.
Depart123
I and my partners have spent a great deal of time documenting this effect. We have taken optics, both rifle scopes and spotting scopes, with verified reticles in them, and mounted them to solid benches or stands. We observed fixed objects across clean air (across canyon) where there was no ground effect mirage.
It varies depending light intensity and the angle of the sun. It was as little as 0.2 mils to as much as 0.5 mils. On days when there was strong sun but heavy intermittent clouds, you could watch the target move up and down against the reticle in real time. The target moves in a direction opposite of the sun, so the target can get pushed sideways as well as down.
After observing this effect for a couple of years now, I have settled on an average of 0.3 mils change for strong sun vs. heavy clouds (light neutral) in my own shooting. The effect being an optical one rather than ballistic, it remains the same angle at all distances. A 0.3 mil (1 moa) change at 100 yds is the same 0.3 mil at 1000yds.
The equation gets complicated near the ground, mirage from ground effect can counteract or add to the effect from the sun alone. A gusty 0-5 wind with strong sun and heavy mirage will constantly be changing the amount of sun push the mirage is counteracting, causing rounds to show lots of vertical spread.
Hope this helps.
A week or 3 ago I was shooting some steel at 900y or so in blazing sun with crazy mirage, everything was going well until I "felt" the sun getting covered by clouds and then all the mirage disappears. My next shot went straight over the steel gong, I thought I must have messed something up, and send another one that sailed over and then the light went on. As soon as the sun came out my poi was exactly as before, so I waited for the cloud cover and quickly fired 3 shots at the gong aiming for the bottom of it and they landed just above my previous group where I aimed for the middle. I always new clouds "shifted" poi but never experienced it like that. That steel gong is a tad over 10inches so the shift was about 5" but the temp/sun was crazy that day so it might have been a little excessive
Reading all the replys here ill also start concentrating on about .4moa change when cloud cover rolls in
Reading all the replys here ill also start concentrating on about .4moa change when cloud cover rolls in
Last edited:
dmoran
Donovan Moran
That is a typical amount - IME
I like big puffey clouds on sunny days at matches. Makes it easier to beat a lot of the field... lol
Donovan
Thanks thats real good to know, we always talk about lights down sights down but no one really tell you how much. In steel matches our targets are around 1moa so its not that hard...clouds roll in aim at the bottom..but ill spend a bit off time with the different paper targets we shoot at longer ranges
This is Good to know
4xforfun
Gold $$ Contributor
Depart123
It depends on the condition you zero'd in. If you zero in strong sun, then you have accounted for the sun push in your zero. When that sun goes away you are now seeing the target where it actually is, so the shots go high. if you zero in heavy overcast (light neutral) it will happen in the opposite manner.
Or, if you zero in a condition where the sun push is canceled out by a lazy rising mirage, you won't see much change either. You have to take note of zeroing conditions in addition to everything else to put the puzzle together.
I'm not a long range shooter but I know a few. I've heard the expression, "Lights up, Sights up". Just saying.
Your not the only one. People are mixing mirage movement of the image with warmer or cooler temps. The saying about sights up and down is used with sling/open sight shooters who adjust their sights for changing conditions.
Depart123
Everyone has heard the expression, though far fewer know it's appropriate application.
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