Mirage - how much point of impact shift?

[Warren Jensen]

Len,

Back to your setup. Your bench and bags should be stable, but don't take it for granted. Conduct a test over several days with sun and shade and temperature changes to ensure that there is not setup movement. Then move out to distance for the mirage tests.

 

[Len Backus]

This discussion from a while ago came to my attention again today.

TTT

 

[codyadams]

Tag.

 

[Tyler Holderby]

I have noticed this the past two years also doing more shooting, keep notes, etc.

Mirage with a boil, direction of thermals with little Mirage present, sun light, sun position. It's interesting stuff.

Make me rethink my max effective range for 1 shot kills while hunting, all these ever changing environmentals compounding and it's a miss at what normally I feel confident at.

 

[BillLarson]

I am trying an experiment. A couple days ago I set up a rifle with its attached 22 power scope aiming at a 700 yard target. I recorded the sight picture at the start of the experiment --- 8PM. I left the rifle out on its setup overnight and through the next day at 4:20 PM.

As you know, the reticle shifted apparent location on the target over time as the sun and wind directions as well as temperature changed.

The target is to the east. At 8PM the sun was from the west behind clouds and a slight wind blew from the west. Temp was 80 degrees.

At 5:30 AM the sun was from about the norhteast and wind was from the north. Reticle was 2 inches right and 2.5 inches up. Temp had dropped to 60 degrees.

At 8:00 Am wind was 5 - 10 from the north. Temp was 65 and reticle was up from original by 5 inches and moved to the right 2 inches. Sun was from the east and now higher in the sky.

At 2 PM wind was 5 - 12 mph from the northeast. Temp was 82, sun was out from the the southwest. Reticle was close to original spot, hard to see in the mirage.

At 3:30 PM wind was closer to north at 5 - 10. Sun was still bright and reticle was at original spot.

At 4:20 the bright sun was from the west, temp was 85. Wind from the north at 5 - 10. Reticle was back up 5 inches from original and but shifting right and left of original by 3 or 4 inches.

I will try this again a little more carefully --- but for now what does it mean?

[ 07-03-2001: Message edited by: Len Backus ]

This same test has been done a few times..... with about the SAME RESULTS..... I used to have a silhouette pic of a fixed gun sited it AM... and hourly throughout the day.... this was at 100 yds. and no wind to speak of.....
The crosshairs were tracked.....and What an Eye opener......