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Thread: How much does temperature and/or humidity change affect point of impact?

  1. #1
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    How much does temperature and/or humidity change affect point of impact?

    I was at the range today shooting my Remington 700 308 Win. (and a few other non-precision hunting rifles). It shot great, nice sub-MOA groups as always. However, my groups were all .5" to .75" higher then usual.

    I last adjusted my zero in mid June when I switched from FGMM 168 gr. to FGMM 175 gr. It was around 65° with no real noticeable humidity or dew point (not that humidity/dew points are too noticeable with 65° temps.). Today it was about 85° with 68% humidity with dew points in the upper 50's with no wind to speak of.

    Would the extra 20 degrees with a little more humidity and higher dew points make the rifle shoot a tad higher?

    Thanks, NYH1.
    Last edited by NYH1; 07-27-19 at 22:35.

    ROLLTIDE!
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    It depends on the powder. Companies like Blackhills use temp stable powders which is one of the reasons it's costs so much. CivilIan/non duty ammo is most likely not temp stable.

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    I shoot factory Federal Gold Metal Match 175 gr. ammo in it. I don't know what type of powder they use.

    Thanks, NYH1.

    ROLLTIDE!
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    Quote Originally Posted by NYH1 View Post
    I shoot factory Federal Gold Metal Match 175 gr. ammo in it. I don't know what type of powder they use.

    Thanks, NYH1.
    Most likely not using temp stable powder. You'll just have to have a cold weather zero and a hot weather zero or get duty grade ammo.

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    I think that thats a reasonable shift for a 20* change. Wouldn’t be surprised even with .mil ammo. Snipers that I have worked with collected temp and altitude data when working up DOPE books for their win mags. Probably more stuff. How they organized that data, I have no idea.

    Sidebar: Mortar ballistic computers take into account all sorts of weather data, and it can make a significant difference.
    RLTW

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    Disclosure: I am affiliated PRN with a tactical training center, but I speak only for myself. I have no idea what we sell, other than CLP and training. I receive no income from sale of hard goods.

  6. #6
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    Different lot of ammo? Temps do change our dope for sure. And it's not uncommon for my .308's zero to all of the sudden be left, right, up, or down during the year. That's just .308.
    "What would a $2,000 Geissele Super Duty do that a $500 PSA door buster on Black Friday couldn't do?" - Stopsign32v

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    How much does temperature and/or humidity change affect point of impact?

    Google - why rifles zero wander. Interesting read.


    You can drop the temp and humidity changes into a ballistic solver and note the poi changes, but not likely at 100.

    Note that temp can change velocity, particularly in temperature sensitive powders. Most ballistic solvers have the ability to input different velocities for different temps and adjust accordingly. 20 FPS is a fair amount.
    Last edited by Send it...; 07-28-19 at 14:52.

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    How much does temperature and/or humidity change affect point of impact?

    If your groups are rising it could be a couple things, either cumulatively or independently. First being mirage, next being powder/barrel temp.

    Humidity gives resistance to the bullet as it travels through the air so you could notice a drop when shooting longer ranges. I really don’t have experience with altitude variation so I couldn’t say for sure without going to my reference material.


    Sent from my iPhone using Tapatalk

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    Quote Originally Posted by Gearqueer View Post

    Humidity gives resistance to the bullet as it travels through the air so you could notice a drop when shooting longer ranges.


    Sent from my iPhone using Tapatalk
    Actually, thats not quite correct. Exactly opposite.


    https://gundigest.com/more/how-to/tr...let-trajectory



    “Well, contrary to common thought, higher humidity results in thinner air. Yes, you read that right. Despite how it feels to walk out into high humidity (the air feels “thicker”), the air is actually less dense. Therefore, it has the opposite ballistic effect that you might expect — a bullet travels easier through humid air.”

  10. #10
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    In addition to powder temp, hot air is thinner.
    RLTW

    Former Action Guy
    Disclosure: I am affiliated PRN with a tactical training center, but I speak only for myself. I have no idea what we sell, other than CLP and training. I receive no income from sale of hard goods.

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