Mirage - Any Rule of Thumb?

[Len Backus]

On a bright, sunny hunting day at 700 yards, what should I assume the target drift from mirage to be in a 5 mph full-value wind?

 

[daveosok]

McMillan has a good explanation and some good reading on how to deal with mirage.
Mirage

I'm sure S1 will have better answers, wait till he posts.

 

[Brent]

Here's something you might find usefull.

 

[Len Backus]

Thanks for joining the conversation, guys.

"Their actual position is always the "upwind" side so key off that." So...how far upwind might the target actually be in the wind I described above. What is the range in MOA that it might be upwind --- roughly?

 

[Guest]

[ 07-11-2003: Message edited by: S1 ]

 

[Len Backus]

In addition to holding left or right for wind drift, how much will mirage affect my shot by making the target appear to move over to one side or the other? What is a typical mirage-induced range of apparent target movement at 5 mph and at 700 yards in bright sunny conditions?

[ 12-09-2002: Message edited by: Len Backus ]

 

[Guest]

[ 07-11-2003: Message edited by: S1 ]

 

[Brent]

Here's what I do Len. If my target is moving about from mirrage, think of it like this, the target being on rubberbands and the air is making the rubberbands stretch out and back depending on how the air movement along the distance to the target. If the air is steady it will stretch and stay there, maybe letting up a little hear and there as the fluctuates giving it that wavering effect and then it will pull back to the upwind side and be still, maybe for only a moment here and there but where it is still, this is your targets real position.

Now that you've centered on this spot don't move the rifle, watch as the bull returns to the center of the crosshair and stops over and over until your sure it's the true position.

Now you have a baseline to moniter the mirrage direction and guage the speed and duration. You can see switches and letups pretty easy now. The predominant condition is the one I use if there is one, it alows me enough time to get off a shot and not have to wait too long for the same condition to fire another. If you always wait for complete letups, you may have to wait for a while.

Fireing while observing/associating the condition your firing in will teach the rest, and the only best thing I can think of is to have a spotter who reads wind better call the shots for you, which might steepen the learning curve some.

Most of my mirrage happens close to the muzzle from barrel heat after about 4 or 5 rounds, it helps to see the air movement up close which has alot more effect than the movement out just in front of the target. Half way down to the target the wind can still kill you too, it's just that the bullet has already made it that far accuratly first so it don't have much time to act on it.
Hope that helps some, just learning myself.

 

[Guest]

[ 07-11-2003: Message edited by: S1 ]

 

[Len Backus]

Well now, thank you both! I think I even understand most of what you said.

 

[Guest]

[ 07-11-2003: Message edited by: S1 ]

 

[Nicholas]

There is another thread going on about reading wind on snipershide
http://216.219.200.59/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic&f=6&t=000086

 

[greenejc]

Mr. Backus, we were taught to use a spotting scope to determine mirrage. If it was about 30 degrees, it indicated a 5-6mph wind, and the wind was in the direction of the mirrage. If boiling, your target was actually slightly lower than the image, if I remember the manual correctly. I don't have it here right now. You would hold for a 10mph drift at a 45 degree angle and a 60 degree angle gave about a 15 to 17mph wind drift. Hold off depended on the load used. Most of this was taught to us using the 7.62 Nato Lake City or Federal Match using the 168, 173 and 175 Sierra Matchking projectiles at a nominal velocity of about 2630 or so from a 24" barrel, 2550 from the M21. I don't know what you were shooting, so hold off would no doubt be different from ours. For us, the windage would have been between 20 and 25 inches at 700 yards, or about 3 to 3.3 moa or about 1 mil. The U.S. Army and Marine manuals cover mirrage and its effects pretty well.

 

[LRNut]

Mr. Backus, we were taught to use a spotting scope to determine mirrage. If it was about 30 degrees, it indicated a 5-6mph wind, and the wind was in the direction of the mirrage. If boiling, your target was actually slightly lower than the image, if I remember the manual correctly. I don't have it here right now. You would hold for a 10mph drift at a 45 degree angle and a 60 degree angle gave about a 15 to 17mph wind drift. Hold off depended on the load used. Most of this was taught to us using the 7.62 Nato Lake City or Federal Match using the 168, 173 and 175 Sierra Matchking projectiles at a nominal velocity of about 2630 or so from a 24" barrel, 2550 from the M21. I don't know what you were shooting, so hold off would no doubt be different from ours. For us, the windage would have been between 20 and 25 inches at 700 yards, or about 3 to 3.3 moa or about 1 mil. The U.S. Army and Marine manuals cover mirrage and its effects pretty well.

I think Len's original question pertained to the effects of light refraction displacing the target, not how to hold for the wind, but it was so long ago, who knows?