Temperature effecting bullet drop

Discussion in 'Long Range Hunting & Shooting' started by ven, Nov 1, 2008.

  1. ven

    ven Well-Known Member

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    Went to the range early this morning to do a bit of practice in preparation for a good winter of long range hunting.
    After a quick 100 yard zero check that was bang on i placed targerts out to 5oo yards.

    All my rounds hit 0.2 mils lower than when i made my drop chart up 4 months ago.Two clicks up put me dead on.

    Now when i made my drop chart the temp was 15 c.this morning it was -2 c could this the cause of my low shots.
    Thanks
     
  2. 4xforfun

    4xforfun Well-Known Member

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    YEP!!!....I checked my infinity program:105 berger @3050. Drop from 65 F to 28 F gives you 1 additinal inch of drop at 500.

    Now, to be honest, not sure exactly what a "mil" is. I am a "MOA" kind of guy.

    Also, and mayby a bigger factor, is that MOST of the time (depending on the powder used) you velosity will be LESS when it is cold. Compare you loads with a chrono at the two different extremes. Velosity loss at cold temps is probably your biggest problem.

    Hope that helps.
     

  3. Willys46

    Willys46 Well-Known Member

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    this is a formula that uslally works for a 308. So yes temp dose effect it. In my 6mm rem used to lose 1 moa at 600 yards between 75 summer and 45 winter.


    At 300 yards there is 1 MOA change in elevation per 20 degree change in temperature.
    At 600 yards there is 1 MOA change in elevation per 15 degree change in temperature.
    At 1000 yards there is 1 MOA change in elevation per 10 degree change in temperature

    This was taken form Sniper Formulas
     
  4. JeffVN

    JeffVN Well-Known Member

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    Yep the temperature difference translates into a lower velocity muzzle and then more drop at any given distance.

    The good news is you figured it out before you hit the hills on your hunt. You should be able to develop a decent per temperature degree drop in velocity based on some of your current data, such that you can predict the drop if its -20C on your hunt.

    My brother has aper degree velotiy drop formula for RL-15 that he uses for his .308. I use an Exbal program that lets me input the temp and other weather conditions - so it does the math for me. Having aback up sheet that predicts behavior gives you the ability to verify the sugggested numbers from a PDA without having to rely entirely on the gizmo to be correct.

    JeffVN
     
  5. eshell

    eshell Well-Known Member

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    Actually, temperature can have a much greater influence than just muzzle velocity, which will depend on the cartridge temperature and the sensitivity of the particular powder to temperature changes.

    Even if muzzle velocity remains constant, temperature affects air density, which affects drag and thus trajectory. I can see swings of 1.5 MOA at 1,000 yards with my 6.5-284 due to changes in density altitude alone.
     
  6. ven

    ven Well-Known Member

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    Thanks for the replys very helpfull.will make up two charts for summer and winter.
    I am so gratefull that i did not go to shoot a deer at 500 and hit it low as i would have done if i had not checked.
     
  7. Limbic

    Limbic Well-Known Member

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    Sat it was 65 and I was dead on.

    Today it was 77 and I was .75 inches high.

    FWIW