Zeroing questions

Discussion in 'Rifle Country' started by Jonny2guns, Jun 12, 2022.

  1. Jonny2guns

    Jonny2guns Member

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    So my range in order to get a 100 yard shot, you are either looking uphill or down hill approximately 12.5°. If I zero at 100 yards uphill, how is that going to affect my zero at horizontal or downhill? IMG_20220611_113656596.jpg
     
  2. CoalCrackerAl

    CoalCrackerAl Member

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    No it wont. My one club goes downhill out to a 100 and the other is flat accross. I did not experace any difference in point of impact.
     
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  3. jmr40

    jmr40 Member

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    I'm not good enough at the math, but the angle will mean the bullet is actually traveling slightly less than 100 yards. Someone smarter than me could calculate the exact difference. But it won't be enough to matter. Just guessing, but if you set your target at around 105 yards that would compensate for the difference.

    And it doesn't matter if you're shooting uphill, or downhill. The actual horizontal distance the bullet travels is somewhat less due to the angle. This is only an issue when shooting at much longer distances, and with much steeper angles. It's actually more of a problem for archery hunters shooting from an elevated stand. If you're 30' up a tree and shooting at a deer 30' away the deer is actually only about 20' from the base of the tree. With the arched trajectory of an arrow that is significant.
     
  4. Varminterror

    Varminterror Member

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    If you are shooting at a true horizontal 100yrds, not just 100yrd line of sight, then the zero will be the same.
     
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  5. trackskippy

    trackskippy Member

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    Math-wise, 100 yards (300 feet), with a positive 12.5° angle, you'll be 66.51' higher than your shooting position at the target (assuming the target is the same height off the ground as the bench, if you''re using one). A straight line distance from the gun to the target is going to be 307.28' (307' 3-3/8" for the carpenters. :)).

    I always get the shooting part of this confused, but I seem to remember if your gun is zeroed on a level plane, you need to start aiming low, past a certain degree, and that goes either way, positive or negative, due to the trajectory curve.

    Im not sure if the answer is here or not, but I use JBM's trajectory calculator for a lot of stuff and its pretty extensive. The answer you seek is probably in there somewhere, if you get to digging. :)

    www.jbmballistics.com/
     
  6. LoonWulf
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    LoonWulf Contributing Member

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    I don't usually worry about degree change at that distance...... So I put it into strelok...
    With my dad 6.5 12° slope equates to 0.1 of an inch difference.
     
  7. Skylerbone

    Skylerbone Member

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    Just make sure of your measuring device, the last 2 generations of range finders I’ve purchased compensate for angle and show the ballistic range rather than actual measurement.
     
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  8. Jonny2guns

    Jonny2guns Member

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    SIG KILO 2200MR.... is that new enough?
     
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  9. Laphroaig

    Laphroaig Member

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    The cosine is the trig function that would give you the answer to your question. If it is 100 yds measured along the ground surface, a 12.5* slope translates to 97.6 horizontal yds.
     
  10. High Plains

    High Plains Member

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    Shoot the same distance in the fall or winter when the temperatures are likely lower. That will make a big difference on a zeroed rifle vs summertime temperatures.
     
  11. jmr40

    jmr40 Member

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    That would depend on the powder used. Some powder will change velocity 2-3 fps for each 1 degree temps change. A rifle tested at 70 degrees could be 140-200 fps slower at 0 degrees. That might make a difference at longer ranges. But most powders anymore are pretty temperature stable and will see 1/2 fps or less change. With that type of powder no more than 35 fps difference with 70 degrees temperature change.
     
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  12. LoonWulf
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    LoonWulf Contributing Member

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    Strelok can use your phones accelerometer to give you the slope also.
    Screenshot_20220612-134254.png Screenshot_20220612-134303.png

    Ive compared it to my RF a few times and they agree perfectly......
    It's also assumes your phone's accelerometer is calibrated properly i suppose..... You don't get asked you to do that anymore, but in a lot of the older apps that used it for stuff like this they did.
     
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  13. Varminterror

    Varminterror Member

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    Your 2200MR can display angle compensated range as well as LOS range. Not really an age thing, some LRF’s have had angle compensation calculators and onboard inclinometers for at least 20yrs.
     
  14. Skylerbone

    Skylerbone Member

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    Thats what I was getting at; if you’ve already been given the compensated range it should be on. If you have the actual range, you’ll be off because of the angle. Just reminding people to know which distance they’re actually shooting at.
     
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  15. taliv

    taliv Moderator Staff Member

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    the bullet is actually traveling 100 yards. what you're thinking is a simplistic way to calculate trajectory for angles is to consider the effect of gravity only over the horizontal portion, which is why the cosign angle doohickies you attach to scopes used to be popular. but unless your projectile is traveling close to the speed of light, it's actually traveling the measured distance
     
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  16. jmorris

    jmorris Member

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    Zeroed horizontal, you will shoot high when you are aimed up or down. Gets worse as the angle becomes greater.
     
  17. jmorris

    jmorris Member

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  18. daniel craig

    daniel craig Member

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    This is the answer
     
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  19. Varminterror

    Varminterror Member

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    Cosine correction is only necessary if the LRF isn’t already doing that math for you. The OP’s Sig Kilo 2200MR (same LRF I use) already has the ability, activated by default, to do this correction onboard.
     
  20. doubleh

    doubleh Member

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    For only slightly over 2 yards I wouldn't bother with any compensation unless it was a benchrest match for money.
     
  21. Jonny2guns

    Jonny2guns Member

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    Varmint control
     
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