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Thread: re-zero for winter?

  1. #1
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    re-zero for winter?

    i have heard changing weather conditions will effect your zero. i zeroed my rifle in the summer when was about 90 degrees with a ton of humidity. between then and now most time spent with my riffle has been spent at 50 yards or less just trying to learn how to run it with some proficiency.

    i had my riffle out this past weekend. it was about 50 degrees and very low humidity. i remembered to check my zero. it had not changed. i mean not at all. i just couldn't find any adjustments i needed to make. i was shooting roughly 3 moa (at 100 yards w/ 2 moa aimpoint) with my preferred ammo that i only really use to test for reliable function and check zero with. and i was happy with it.

    from 90 degree summer heat to 50 degree fall/early winter weather..... i was pretty sure my zero should have done something. right?

    do you change you zero for the changing seasons? should i consider my zero GTG, or wait until it hits 20 degrees and THEN check it? when do you see your zero shift? how dramatic is the shift you find in your zero? is it possible my zero HAS shifted but it is too small to notice at 100 yards?
    Last edited by kenndapp; 11-19-12 at 22:13.

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    I think it is just too small to notice at 100 yds. Lost inside the 3 MOA spread you are shooting. For a precision rifle at 400-1000 yds. Definite difference. For an combat-accurate AR...not so much a factor.

    I could see checking if there is a summer to dead of winter difference. Might need to go up a MOA or 2 when it is below freezing from a 90 deg. zero.
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    Yep... hardly noticeable on an AR inside of 300 or so.

    We developed bolt gun loads last winter and when summer kicked in, all our bullets were flying over the target.
    "You people have too much time on your hands." - scottryan

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    that what i thought. thanks guys. i am going to take the time to check again when it hits 30 or 20 degrees. but your right. if there is a shift it is lost inside my 3-4 inch groups at 100 yards. wonder if i will need to make an adjustment when it gets really cold.

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    Verifying/re-zeroing is needed always when the weather changes.

    Actually it is not the outside temperature that matters, but the temperature of your ammunition. Cold powder will result in less pressure and slower muzzle velocity. How much, it depends on caliber and powder type.

    With Vihtavuori N1xx powders the magnitude is 0.2% in MV(0) per every degree Celsius. Say you zero in at 100m in the summer (+20C) and then hunt in the cold winter weather (-20C) you will get a reduction of 8% in the muzzle velocity. That is very significant IMHO.

    Always verify and re-zero if the weather changes are big.

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    Quote Originally Posted by Jippo View Post

    Actually it is not the outside temperature that matters, but the temperature of your ammunition. Cold powder will result in less pressure and slower muzzle velocity. How much, it depends on caliber and powder type.

    Granted there are some powders that are pretty temp sensative, there's a lot of info that contradicts this. I mean.. I've seen the Davidson brothers put one round in the sun and one round in an ice chest and shoot them same POI.

    Barrel temp is the biggest factor. I was reading an article (I forget where now - I think accurateshooter..?) about barrel temp regulation. And the gist of it was... if you're not regulating your barrel temp, precision powder measurements don't matter.
    "You people have too much time on your hands." - scottryan

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    Learn something new everyday, never considered this, but since I live in the glorious state of CA, southern CA, I do not have to worry about it. Just have to check the laws daily to make sure I do not have anything new that would make my already neutered AR an "assault rifle," cause then I might want to murder children....


    But say if temp in the rifle rises would the "winter zero" then change as the rifle is no longer cold?

  8. #8
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    Non-precision gun, short(er) ranges, you won't notice any deviations of concern.
    Last edited by ST911; 11-20-12 at 12:35.
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  9. #9
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    Quote Originally Posted by Zane1844 View Post
    But say if temp in the rifle rises would the "winter zero" then change as the rifle is no longer cold?
    On thinner profiled bolt gun barrels you can see the POI walk up on the target as the barrel gets hot.

    On an AR, the groups will usually just open up.
    "You people have too much time on your hands." - scottryan

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    Quote Originally Posted by Skintop911 View Post
    Non-precision gun, short(er) ranges, you won't notice any deviations of concern.
    does 1-300 yards meet your definition of "shorter ranges" ?

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