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Mirage and temperature.

 
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  #1  
Old 11-19-2005, 10:08 PM
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Location: Shoshoni, WY
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Mirage and temperature.

I did a search and I can't find much information about the effects of mirage and the effect of temperature on the burning rate of powders. I have Exbal on a pocket PC so most environmental variables are something I can correct for. Just out of curiosity, do you guys chrono your loads at various temperatures? It seems to me plugging in the air temp in Exbal is dandy, but are air density changes due to temp as important as changes in burning rate.

I am also curious how you guys correct for mirage? I hunt a lot of varmints in hot dry weather and I know the effects of mirage can be substantial. The same can be true in the winter when it's bitter cold. What's the secret?
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  #2  
Old 11-19-2005, 11:26 PM
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Re: Mirage and temperature.

Ankeny,

RE: Temp and powder burning rate. Some powders are more temp sensitive than others. RL-22 seems to be plenty temp sensitive. I loose about 130 FPS from summer to winter on one rifle and a bit less in another.

Its a pain to have winter and summer loads. Can't seem to keep them sorted out. Winter loads are way over pressure on 85 degree days.

RE: Mirage. Just finished developing a drop chart this morning. Nice warm 40s, slight wind. Much mirage. I got so confused I was holding exactly opposite as to what I should have several times. [img]/ubbthreads/images/graemlins/frown.gif[/img]

Here's how ya do it: shoot-shoot-shoot-swear-shoot-swear-shoot-shoot shoot-swear.
Do that for several years and pretty soon you kinda catch on. [img]/ubbthreads/images/graemlins/smile.gif[/img]

Then you're all confident and you head for the range/dog town/chuck spot etc. Then it goes something lik this: shoot-shoot-shoot-swear-shoot-swear-shoot-shoot shoot-swear.

Who's signature line says something like "cause anyother sport wouldn't be so frustrating" or something like that. [img]/ubbthreads/images/graemlins/grin.gif[/img]

At 540yds today either the target or the bench was shifting 4" left and right. And the bench is solid as a rock [img]/ubbthreads/images/graemlins/mad.gif[/img]
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  #3  
Old 11-20-2005, 06:07 AM
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Re: Mirage and temperature.

Yes, it is incredibly useful to chrono your load through the year and get the altered Vo.
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  #4  
Old 11-20-2005, 08:04 AM
 
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Re: Mirage and temperature.

Roy in Ideeho

<<At 540yds today either the target or the bench was shifting 4" left and right. And the bench is solid as a rock>>

Hehe!! This tells me you were shooting in what's known as a "fishtailing" condition aka where the wind is either coming in from 12 or 6 o/clock and shifting back and forth from side to side! When shooting LR HP competition I use to love this condition because that was my forte!! To shoot good scores or to hit what you're shooting at under this condition you've got to watch the mirage flow continuously and learn to break the shot accordingly...under the same condition. I would pull my spotting scope up close to my shoulder so I could monitor the mirage flow...while watching the downrange flags and when I got the condition I wanted...I'd roll over to the rifle and quickly break the shot! I might add however that under this condition/wind....the mirage is MORE IMPORTANT than the flags if available! There will be some point under this condition whereby the mirage will appear to come to a "boil" and it's advisable to NOT SHOOT under this condition UNTIL the mirage flow settles back down to one side or the other! Under other condtions of mirage flow than a fishtail condition...a boil is the first indicator of an imminent change forthcoming! The mirage will either continue to "boil" if the wind remains from the 12 or 6 o/clock position or....it will swap toward one side or the other! Under conditions of minute change involving a fishtail wind you may find that rather than taking the time to "twist the knobs" to counteract the drift that it's more advisable to "favor" with the crosshair aka "hold off" toward one side or the other depending on the flow direction! I might also add that one doesn't need to be a "Rocket Scientist" to learn how to do this but it does involve burning enough powder to become effective to shoot under these conditions!

Hope this helps!
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  #5  
Old 11-20-2005, 08:42 AM
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Re: Mirage and temperature.

[ QUOTE ]
aka "hold off" toward one side or the other depending on the flow direction!

[/ QUOTE ]

Appreciate you input. When I was shooting benchrest comp. I did pretty much the same thing except with a highpower scope I didn't need the spotter. However, I always got mixed up at times. I think its my natural inborn lack of patience [img]/ubbthreads/images/graemlins/frown.gif[/img]

My trigger is a bit sucky and needs changing and causes shots to go left or right at times. It varies in pull from light to heavy from shot to shot and you never know which until its time for the shot. I think that added to the problem.
I was shooting over sand, pasture, about 350yds of swamp then more pasture. Wind was angling towards me, say I'm 0 degress (north) (or 12:00)wind was from nearly south but a little to the west say from 200 degrees (or 7:00). Max speed was less than 5 MPH.

Mirage would run to my left, boil at times and at other times would run to my right but not as strong as to the left.

I know not to shoot during a boil but some time just can't resist. Thus the swear [img]/ubbthreads/images/graemlins/grin.gif[/img]

Shooting a 250 grain bullet at 2800 fps mv that amount of wind was pretty much non-existent, I think....

Here's the dumb question:

Should I hold opposite the mirage or with the mirage. Pretty much backwards of holding into the wind? In benchrest shooting it didn't make any difference where the group was just so it was a group. This is a whole different story.

Thanks for your patience.
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  #6  
Old 11-20-2005, 09:26 AM
 
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Re: Mirage and temperature.

If the mirage flow is from 9 o/clock (left to right) THAT is the direction of wind flow so you hold left...into the wind!
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  #7  
Old 11-20-2005, 12:48 PM
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Join Date: Jul 2005
Location: East TX
Posts: 773
Re: Mirage and temperature.

[ QUOTE ]
Ankeny,

Here's how ya do it: shoot-shoot-shoot-swear-shoot-swear-shoot-shoot shoot-swear.
Do that for several years and pretty soon you kinda catch on. [img]/ubbthreads/images/graemlins/smile.gif[/img]

Then you're all confident and you head for the range/dog town/chuck spot etc. Then it goes something lik this: shoot-shoot-shoot-swear-shoot-swear-shoot-shoot shoot-swear.


[/ QUOTE ]

That is hillarious and soo true.
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