Shooting downhill POI?

Discussion in 'General Discussion' started by J.G.W, Sep 8, 2018.

  1. J.G.W

    J.G.W Well-Known Member

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    Now I understand that when shooting downhill (or up) you need to aim for the horizontal distance to the target rather than the line of site distance but at what range and angle will this actually have an effect on point of impact? For instance if I was shooting at a target 100 yards away and 30 feet lower would there be a noticeable change in point of impact from a perfectly level 100 yard shot?
     
  2. kiwikid

    kiwikid Well-Known Member

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    If you were to use a rangefinder with an EHR (equivalent horizontal range) program you would see that there would be a slight difference between the line of sight distance and the horizontal distance. If it wasn't dark outside I would take my rangefinder out so i could give you an idea of what the difference is. I would expect however that the difference would be small at the figures you have suggested, maybe 3 yards.
     
  3. Hatrick

    Hatrick Well-Known Member

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    The further you shoot and the greater angle makes much more difference. Shooting 400yds up or down at a 45' angle would be like shooting 200yds. If not corrected you would shoot way high.
    Fortunatly almost every new range finder does this for you.
     
  4. ShtrRdy

    ShtrRdy Well-Known Member

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    For a distance of 100 yds it wouldn't make much/any difference. This is because on a typicall 100 yd zero the bullet is reaching its highest point +/- around 100 yds.

    For a longer shot with uphill/downhill angle an improved method is to multipy the cosine of the angle with the drop correction for the line of sight distance. The best approach is entering the angle into a ballistic calculator and coming up with a unique solution.
     
  5. J.G.W

    J.G.W Well-Known Member

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    AFDBF5C5-C175-4304-A988-E478ED36CB5E.jpeg 5973BC41-C980-400A-BC30-67644DB5DD30.jpeg Thanks. The reason I ask is I set up a range close to my house on the weekend, there is some fall from bench to target and I was just curious as to what the effect would be. Fall is roughly 30 feet at 100 yards and 60 at 300. In reality when would you get a perfectly level shot at an animal anyway.......... never.
     
    Last edited: Sep 10, 2018
  6. Hatrick

    Hatrick Well-Known Member

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    Gravity is always straight down so all you need to do is find the third leg of a right triangle. (One with a 90' angle)Your 100yd shot will be 99.5yrds and your 330yd will be 329.9
     
  7. ATH

    ATH Well-Known Member

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    Effect at 100 yards is negligible except perhaps at extreme angles. Last year I nailed an elk at 730 yards and 1000ft elevation above me. This particular calculation was kind of important.
     
  8. BallisticsGuy

    BallisticsGuy Well-Known Member

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    If you're trig fluent the answer is, multiply by angle cosine. Otherwise, look at an angle cosine indicator or protractor with cosine markings and you'll see. Depends on the AHR to the target but in general I don't account for slope until I'm past 10 degrees up or down angle unless the shot is REALLY long. By 20 degrees you're around the .90xAHR mark where I'd start making adjustments almost regardless of AHR.
     
    Last edited: Sep 15, 2018
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  9. Barrelnut

    Barrelnut Well-Known Member

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    You can judge angle by extending you arm horizontal toward the target and making a fist. The size of your fist is about 10 degrees at that point. Then just measure with the number of fists from horizontal plane to the the target. As in: 3 fists would be 30%.

    The easiest and quickest way to figure how the angle affects the shot is to use a ballistics app on your phone. Shooter is great and inexpensive. Then you can calculate the shot in Shooter with no angel and again with the angel accounted for and you will start to get a good feel for how an angle will affect a shot and at what distances.

    Then you will be able to use your fist in the field to quickly determine if you need to account for angle measurements.
     
  10. yobuck

    yobuck Well-Known Member

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    For bench shooting as stated where you would primarily be shooting for group, it matters not where the group is with regard to the exact aiming point.
    Lots of things can alter that and it might vary from session to session. Up/down angles aren't much of an issue unless your shooting in steep mountainous terrain especially when hunting. Best solution is to practice shoot as much as possible so as to get a feel for what happens. By and large a slight hold change on the target will suffice.
    But there is no doubt that serious angles at long distances can have a big affect on your hitting what your aiming at, and that can be critical when hunting. There are numerous good methods for determining the information and some have been mentioned. Fact is though some of us cant get enough of modern techknowledgy, and some of us want as little of it as possible.
    I have a small device I can put in my shirt pocket if I remember. Its a type of protractor, but designed strictly for angle shooting. When my tripod mounted glasses or the gun is aligned on the target, I can just hold that on and it gives the angle and the percentage difference in yards. It's called a Slope Doper, but frankly we rarely use it.
    Virtually all PA l/r hunters use the buddy spotter system, and some also rely on a sighter shot of some type.
    Remember this when hunting in steep terrain, the precise information you gathered can be obsolete before you even get a shot off, especially during the rut.
     
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