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Temperature !

4K views 4 replies 5 participants last post by  Shadow Five 
#1 ·
Hi guys,
Case: .308Win. Assume the starting speed of 840m/s. Range 600 meters. Now the guy calculated that at 25 degrees celsius POI will be 5 cm higher than at 15 degrees celsius (optimal temperature for shooting). Now, he also calculated that since the air is 10 degrees higher the powder will burn faster thus causing the bullet to travel 849 m/s. That speed will now cause POI to be 9 cm higher at 600m. Than he do the math and said : 5+9=14 cm. So he concluded that POI will be 14cm higher at every 10 degrees increase at 600m!!!At that range 14 cm = 0.91 MOA. Sounds resonable. But I would like to know is there any temperature tables I could refer to when calculating temprature infulence on a bullet.
Second, he said that direct wind blowing 10 m/s will cause the bullet to slow down from 840 m/s to 830 m/s. I wonder how that affects POI on a target. I know it's small difference but still.
 
#2 ·
Every rifle I own and every powder I have shot with a starting temp of 90* loses 1 MOA @ 1000 yds for every 10* temp drop. Example:

My .308
90* 32MOA ^ for 1000 yds
80* 33MOA ^ for 1000 yds
70* 34MOA ^ for 1000 yds
60* 35MOA ^ for 1000 yds
50* 36MOA ^ for 1000 yds

I shoot to 1000 yds every weekend. I plot my impacts and keep a detailed record of come ups required in each temp swing. I have used 3 different powders in this rifle behind the same bullet and get the same results. I see the same trend in my .260 and my 7WSM also. Anyone that tells you they have 1.5 MOA swing from 30* to 90* is straight full of it or they just aren't shooting the same load out of the same rifle in each temp range. I have verified my results with 2 other long range shooters and they have the same results. These other 2 shooters also shoot 1k very often. One of them even owns a 1k range and has been shooting on it for 25 years.

I have read 1 guy on another site talking about his IMR 4064 only having a 2MOA or so swing from freezing to 90*. This is the same guy that comes to the match and shoots a "5" for a total score. Yeah, like I am going to believe that! :roll:

Ask the guys that shoot LONG range on a regular basis and are at least 1/2 way good at it and they can tell you. I am fortunate to shoot with someone on the US Palma team and he has a bit of talent to back up his data. After he makes a claim about something he pics up his rifle and prooves it. Like when he told me he was shooting a 210gr bullet @ 2710fps out of a .308. Now note he does have a 30" bbl but still! Well... he is... and he wins with it too. Look in the recent Berger catalog and you can see some pics of the guy and read a little about him.
 
#3 ·
Want to do something really weird. Set up your target and pull your rifle out of nice heated car and shoot it right away "withing 1 minute". Leave your rifle outside for about 30 minutes and than shoot it again. Do this at about 500 yards or more and you will see a change in bullet impact. It's not so much temperature that changes POI, it's a multitude of thing's that can really throw you off especially when you have 2 of them against you. Say you don't adjust for altitude and temp. Them 2 together will cause you to miss completely when shooting at long distances. Get good at math and learn the formulas and you will be good to go. If you are suffering in math purchase a calculator until you get good at it.
 
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