Range Report effects of sun and/or mirage on POI

[GrantB]

I would like to know if others have seen the same thing.

The test:
100 yards 260 Defiance fully custom gun using NF nsx 5.5-22. I used one point of aim for both groups. Each day I would shoot 2 shots at the same POA from the same position. I started with a dirty barrel and didnt clean at any time during this test. First shot of the day was at 0645 hours while the sun was still below the tree line. The second shot was at 1500 hours in full sun (if there was a cloud overhead I would wait until the sun came out again.

The verables were sun, mirage and Tempitaure only, I tried to control everything else.

The results: After shooting 2 shots a day for 5 days I had 2 perfect and concise 5 shot groups. the first and upper group measured .38" and the 2nd group measured .41" and they were .6" apart in the vertical direction only. The upper group were the shots at 1500 hours and the lower group were the ones fired in the morning.

I'm sure there was a velocity change from cold to hot (about 20deg) but I've checked my POI with a 50 degree change many times and I couldn't tell any difference in the POI at 100 yards before.

Could the .6" vertical @ 100 yards be all or mostely caused by the sun shining at different angles on the target and the mirage affect.

 

[MD2Colo]

did you adjust the scope's obj or ocular at all after shot 1?
Yah, mirage can definitely be a pain at greater distances when conditions are right for it. I've just kinda quartered the best i could and held for wind then let her fly.
I read somewhere that to test this apparent poa/poi shift thing you can grab your spotting scope, set up something at like 800 and get your good quartered tgt poa in the morn, then as the mirage grows go back later and observe any shift.

Never done it, but I'm willing to bet that your poa will sink a little bit towards the ground as the mirage grows.
Just a guess. Interesting test, though.

So yah, did you adjust your scope at all?

 

[kraigWY]

Could the .6" vertical @ 100 yards be all or mostely caused by the sun shining at different angles on the target and the mirage affect.

Maybe, low light often makes some people shoot low in bright light and high in dull light.

General rule, hold or click into the light. How much depends on the shooter and the shooter's eyes.

 

[wilecoyote]

iron sights rule of thumb: light up = click up / light down = click down
(never really understood if can work w.scopes,too)

 

[308boltgun]

Light up - light down sight down primarily aplies to service rifle with a post sight. When the light is low the shooter has a tendency to push the sight into the target. (Assuming 6 oclock hold)