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Thread: Difference in trajectory from Hot to Cold weather

  1. #1

    Difference in trajectory from Hot to Cold weather

    I shoot a 300 Win. Magnum and Iím a little confused. Iím at 4100 feet elevation and in the summer when its 95 degreeís F. I load a 180 Gr. HPBT Sierra #2220 with 73.3 grains of IMR4831 and can hit a 50 cent piece at 200 yards every time. Now that itís cold 37 degreeís F. Iím shooting about 2 feet high I thought it was the other way around you shoot farther when itís Hot and shorter when itís cold but itís the opposite whatís going on?

  2. #2
    i too am a little confused
    slowly slowly catch a monkey..

  3. #3
    I am very confused
    Victory goes to the player who makes the next-to-last mistake..

  4. #4
    Motorbikes seem to get quicker on cold days too. I think more important is the humidity, something to do with causing an explosion in dry/damp air. Water doesn't compress as easily as air/gas. Jet fighters carry water to inject into their engines for extra boost.
    So,,, when you ignite powder on a damp day there will be more pressure driving the bullet, thereby sending it out faster & further, before gravity has its evil way with it.

  5. #5
    Do you have a chronograph? It could be because your velocity is dropping with the colder weather. The low velocity with the slow powder and heavy bullet would cause a higher angle of departure: the barrel is tipping up more before the bullet leaves.~Muir

  6. #6
    I think someone has been messing with your scope!

  7. #7
    Quote Originally Posted by Sausage Warrior View Post
    Motorbikes seem to get quicker on cold days too. I think more important is the humidity, something to do with causing an explosion in dry/damp air. Water doesn't compress as easily as air/gas. Jet fighters carry water to inject into their engines for extra boost.
    So,,, when you ignite powder on a damp day there will be more pressure driving the bullet, thereby sending it out faster & further, before gravity has its evil way with it.
    Sorry Sausage you have got it wrong. Both internal combustion and jet engines burn fuel with air & water pulled in from the atmosphere. Cold and damp air is denser than dry & hot air . There is more oxygen to burn the fuel and the water expands when it boils in the combustion chamber. That is why they develop more power in cold wet weather. Bullets get their energy from powder which has all the fuel and oxygen inside the cartridge. Higher temperature I believe invariably gives higher pressure on ignition so bullets travel faster up the barrel. Both cold and wet air have more slowing down effect on a bullet in flight than warm dry air.
    Muir's comments explain good reason for high bullet point of impact.

    Ian

  8. #8
    A big difference in temperature like that could cause everything to shrink. This might well mean the bore of the barrel reducing in size, and hence increasing your max pressure and giving an increase in velocity.

    I'd definitely be thinking in terms of some kind of differential expansion/contraction effect. Is your barrel floating (if it's fixed down the barrel the contraction might cause a slight upwards curve in cold weather)

    There are a few reasons I can think of, all depending on the exact model and conditions.

    As for cold/damp air, the moisture level is irrelevant (in shooting and in IC engines) The lower temperature increases the density of the air, so more oxygen is available per unit volume. As the air cools, it's capacity to hold moisture reduces, so colder air is actually generally dryer than warmer air.

  9. #9
    Quote Originally Posted by matt_hooks View Post
    A big difference in temperature like that could cause everything to shrink. This might well mean the bore of the barrel reducing in size, and hence increasing your max pressure and giving an increase in velocity.

    I'd definitely be thinking in terms of some kind of differential expansion/contraction effect. Is your barrel floating (if it's fixed down the barrel the contraction might cause a slight upwards curve in cold weather)

    There are a few reasons I can think of, all depending on the exact model and conditions.

    As for cold/damp air, the moisture level is irrelevant (in shooting and in IC engines) The lower temperature increases the density of the air, so more oxygen is available per unit volume. As the air cools, it's capacity to hold moisture reduces, so colder air is actually generally dryer than warmer air.
    Dicing around with the relative humidity and temperature settings on a ballistic program will give some eye-widening changes in ballistics. I live and hunt in extreme temperatures: From 105F to -40F and believe me, at severely cold temps nothing works right, but mostly the powder and ignition. This is one of the factors considered when you hunt somewhere other than your home and are advised to re-sight in your rifle when you arrive at your hunting locality. Also why max loads in the winter months will flatten primers in the summer.~Muir

  10. #10
    I'm not an expert but could be barel harmonics have changed as the temp dropped ( could be wrong, infact probably wrong) it's something to consider.

    What happens to the point of impact if you keep the rounds next to you body for a 20 minutes or so then shot them?

    When I use to chuck 155mm pills out of a rifles barrel we always had to read back the charge temp to the CP before we were given the windage and elevation.

    Jason

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