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Extreme Long Range Hunting & Shooting (ELR) Over 1,000 Yds.


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temperature effect

 
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  #8  
Old 11-12-2012, 05:20 PM
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Re: temperature effect

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Originally Posted by bman73 View Post
So I guess a temp swing of that amount really doesnt have much effect on trajectory at all then at these ranges, or is it more a case of the bullet I'm using just being that efficiant and not really caring all that much about really anything that gets thrown at it.
Well, not too fast here. I just noticed I used Fahrenheit, you used Celsius. We both used 15* difference but I have a feeling that your 15*C is a lot larger difference than my 15*F. My app does not do C so I am not sure we have an accurate answer yet.

Jeff
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  #9  
Old 11-12-2012, 05:35 PM
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Re: temperature effect

According to an online calculator -8c = 17.6f, 6c = 42.8f. A difference of 25.2f
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  #10  
Old 11-12-2012, 07:12 PM
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Re: temperature effect

You definitely should have noticed a difference in POI with a 14 degree Celsius temp change, about 7 or 8 inches according to my calculations. If you noticed none, then something else was at play here.
Aerodynamic jump is the spin related vertical component of a crosswind and we've seen it on many occasions and always allow for it beyond 1000 yards or in strong winds. Bryan covers it well in the chapter on wind deflection in his second book, but his AB program doesn't allow for it unfortunately, so you have to do a simple fudge factor.
The simple allowance we worked out from Bryan's info is .3 MOA for every 10mph of full cross wind, taking it off for a 3 oclock and putting it on for a 9 oclock. It seems to be approx the same for all calibers and bullets. Maybe Bryan can come on and verify if we've got this about right? It certainly seems to work for us.
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  #11  
Old 11-12-2012, 07:15 PM
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Re: temperature effect

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Originally Posted by HARPERC View Post
According to an online calculator -8c = 17.6f, 6c = 42.8f. A difference of 25.2f
Great Thanks! So lets run these numbers again using those corrections.

338 LM / 300 gr Berger @ 2800 fps. ALS 4100 ft.

17.6* F dial up = 29.5 MOA
42.8* F dial up = 29. MOA

a difference of .5 MOA or about 6 inches difference in point of impact.

Jeff
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  #12  
Old 11-12-2012, 11:42 PM
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Re: temperature effect

Jeff you're right. I originally ran the numbers at sea level for 7.5" as I couldn't remember what altitude Bman was shooting at. Just ran them again at 4000' and got a 5.7" difference. Almost 2" difference between seal level and 4000' for the same 14 degree Celsius temp change - interesting!
Greg
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  #13  
Old 11-13-2012, 01:34 PM
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Re: temperature effect

I was hunting last weekend and the shot would have been just over 1000ys. I ran the Sierra and the G7 program which gave me a .25 moa change for every 10 degrees change in temp. I did not try to factor any wind in the program.
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  #14  
Old 11-17-2012, 12:57 AM
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Re: temperature effect

I guess I can chalk up my not noticing much of a difference to my level of inexperience at these ranges then. I am shooting at roughly 2400 feet above sea level by the way, forgot to mention that previously, sorry. I have noticed that I am getting better at this but I am thinking that in order to get to the next level as far as my abilities go I am going to have to start using a rear bag instead of just my fist under the stock. It works great at shorter ranges but not as consistent as I want/need to be at extended stuff. Thanks to all for answers posted on this. Will definately being paying more attention to temp changes from session to session and keeping a better log of corrections for temperature made at the range
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