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How does shooting on a downward or upward angle effect your point of impact?

Discussion in 'Rifle Country' started by blackops, Jun 23, 2009.

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  1. blackops

    blackops Member

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    So many people have different concepts of how a bullet is affected by angle. However, there can’t be more than one correct answer here. I don’t know the technicalities of the whole thing, but from what I understand (and I could be wrong) is that whether your shooting up or down you want to shoot as if your range from the target is as if you were to look straight forward and made a 90 degree angle up or down towards the target and that straight yardage mark should be the yardage you shoot. Shooting up obviously has a little more discrepancy since you’re dealing with gravity, but not enough to make that big of a difference unless you’re shooting at ranges up to 400 yds. Anyways, just wanted to hear what people had to say and try to pull the truth out of the topic.
     
  2. lipadj46

    lipadj46 Member

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    Last edited: Jun 23, 2009
  3. Float Pilot

    Float Pilot Member

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    A.
    x
    x
    x
    x
    x
    x
    x
    x
    x
    x
    BYYYYDYYYYYYYYYYEYYYYYYYYYYYYYYYC[/B]

    You have it right. At steep angles the force of gravity between A and C is the same as between C and B. So the trajectory for shooting from the top of the cliff (A) to a target at point (C) is the same as it would be from B to C.
    Shooting at closer targets from the cliff such as D and E call for shorter range holds since they are only the same as shooting from B to D or E.
    And of course shooting from A to B is a point blank (no hold over range).
     
  4. blackops

    blackops Member

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    I know I tried to locate the thread, but couldn't find it.
     
  5. lipadj46

    lipadj46 Member

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    Sorry it was in the other forum I posted the link above
     
  6. MCMXI

    MCMXI Member

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    Here's an example ... let's say you're shooting at a target 500 yards away at an angle of 20 degrees above horizontal using Federal Match .308 Win 168gr ammunition. According to the ballistic software I use (100 yard zero, standard conditions) here are the bullet drops at the target for three distance/angle combinations. If you use your method above, in this example you'd be shooting about 5" high if you assumed the target is equivalent to being 470 yards (horizontal) away. However, that may be close enough depending on what your objective is.

    [​IMG]


    The reason why a bullet drops less when shot at +/- angles (compared to horizontal) is that the component of the gravity vector (G) acting perpendicular to the path of the bullet (Gperp.) is less than G. The component of the gravity vector G acting along the path of the bullet (Gpara.) has no effect on bullet drop. Only Gperp. causes the bullet to drop perpendicular to the bullet's path. In the example below with the same 20 degree incline angle, Gperp is 30.3 ft/s^2 which is less than G (32.2 ft/s^2). Since the time it takes for the bullet to reach a target 500 yards away, either horizontally or at the given angle, is essentially the same, the bullet fired 20 degrees up experiences less gravitational force perpendicular to the path of the bullet between the muzzle and the target and therefore drops less.

    [​IMG]

    :)
     
    Last edited: Jun 23, 2009
  7. Badger Arms

    Badger Arms Member

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    "Aim low" when pointing low or high.

    All the calculations in the world won't do what a little experience and "Kentucky Windage" will do. This is, of course, unless you take a tripod, 360 degree level, scientific calculator, thermometer, anenometer, humidistat, chronograph, and rocket scientist into the field with you!
     
  8. Art Eatman

    Art Eatman Administrator Staff Member

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    If Bambi is at (or less than) 300 yards, and the angle is 30 degrees or less, don't worry about it. Although the bullet thinks it's only going 86.6% of 300 yards, the lesser amount of drop is trivial.

    At 45 degrees, it becomes more important, at 70.7% of the distance. Gotta hold low for the difference in drop between 300 yards and 212 yards. For an '06 zeroed at 200 and a normal 6" holdover, you'd hit some five inches high. Approximately. :)

    IOW, the cosine of the angle, times the actual distance = the shooting distance.
     
  9. junior geezer

    junior geezer Member

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    in either instance, the bullet's impact is higher.
     
  10. MCMXI

    MCMXI Member

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    That should be NASA's new slogan!! Seriously though, the validity of that comment depends entirely upon the application. Why not present an accurate explanation so that each individual can make an informed decision as to whether or not they need to consider this "stuff" at all? That seems to be the OP's intent.

    :)
     
  11. blackops

    blackops Member

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    A---------1----------2--------3
    x
    x
    x
    x
    x
    xxxxxxxxxxxBxxxxxxxxxCxxxxxxxxD

    Bear with me here. You guys start drawing graphs and mathmatical equations and obiously people have a little more experience than me. lol Say the yardages are as is: A-1=50yds A-2=150yds A-3=200yds Then no matter my angle I will shoot to those yardages. A-B=50yds A-C=150yds A-D=200yds I'm guessing I'm way off here though.
     
  12. ~z

    ~z Member

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    Remember the Pythagorean Theorem?
    That’s all this is, basically gravity acts on the horizontal distance the bullet travels. Therefore the measured distance from you to your target multiplied by the cosine of the angle you are shooting will give you the approximate distance. I say approximate because 1858 is EXACTLY right with the diagrams. If you want to be EXACTLY right with the first shot then use all the tools at your disposal.

    KY wingage and KY jelly often just make a mess when you are unsure of how much to use

    ~z
     
  13. Uncle Mike

    Uncle Mike Member

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    D
    =
    =
    =
    C
    =
    =
    =
    B
    =
    =
    =
    (A).......100y........200y.......300y.......400y.......next zip code

    Just pretend(Really, I'm sorry) that you are at position (A) for EVERY shot you take. It's that simple!

    No matter if you are really at position B, C, D.

    Example-
    For this purpose... If you shoot from D to 400y the bullet will act(because of gravity)as if you were shooting from (A) to 400y.

    If you are perched at B and shooting to 200y, then the bullet is going to act like it was shot from the (A) to 200y.

    It does not matter where you are on the B, C, D side of the scale, the bullet thinks it is always PARALLEL to LEVEL ground.

    Bullet's are dumb... they don't care how high above or low below the target you are, they think they are on the same level as the target is... all the time...stupid bullets.

    :D
     
    Last edited: Jun 24, 2009
  14. PT1911

    PT1911 Member

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    zeroed at 50 yards I can shoot a squirrel 50 yards away in the head whether it is up a tree or I am...

    seeing as gravity works on all things equally, other than at great heights where it is a fraction less, the angle of the shot should have no bearing whatsoever on the point of impact. the bullet drop from point of aim will be the same no matter your angle (for all practical purposes..)

    that said, if you are shooting straight up or straight down the ballistics change. This lends itself to the idea that at a certain (very steep) angle and longer ranges the bullet acts a little differently. I will just be sure to keep my intended target on this side of the peak of my bullet's trajectory.. hit the target every time...:D
     
  15. ~z

    ~z Member

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    “the angle of the shot should have no bearing whatsoever on the point of impact. the bullet drop from point of aim will be the same no matter your angle (for all practical purposes..)”

    Well yes, however I believe you are overlooking one crucial point, distance. The math tells the truth and the physics explains the answer.

    I don’t think I understand your comment, “I will just be sure to keep my intended target on this side of the peak of my bullet's trajectory”…can you elaborate?

    ~z
     
  16. Float Pilot

    Float Pilot Member

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    It really makes a difference when you are using an M-203 on a steep hillside.
    It also makes a huge difference with any arcing trajectory type cartridge.
    Within hunting ranges, not so much with higher velocity rounds.

    Growing up, our daily entertainment was shooting anything floating (drift wood, ice chunks ect,) in the bay from the edge of a 600 foot high bluff. After a few years of doing that with a single shot 22. you get pretty good at guessing the hold under or hold over.
     
  17. MCMXI

    MCMXI Member

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    Exactly! For many angles, many distances and many targets, the difference in bullet drop is meaningless but that doesn't mean we shouldn't think about or consider the implications of shooting angle, shooting range and caliber. For someone to state that the shooting angle is meaningless for ALL applications is just plain ignorant. For example, how about a US sniper in the mountains of Afghanistan shooting a .300 Win Mag and trying to hit a man-sized target 1000 yards away at a positive incline of 20 degrees relative to horizontal. This seems like a realistic scenario so should he use "Kentucky Windage"? I think not.

    [​IMG]

    In this example, the bullet drops 20.3" less (about 2 MOA) at 1000 yards (+20 degrees) so if he was aiming for a center of mass hit, he's just put a round over his target's head. If he uses the "trick" of assuming the shot is the same as a horizontal shot at 940 yards, he's put a round 47.2" (about 4 MOA) over the target's head. Either way, he MISSED and that's with a relatively flat-shooting .300 Win Mag ... a .308 Win and Kentucky Windage at that range would be embarrassing. There are many opportunities for shooter error when making long shots, bullet drop doesn't need to be one of them. If you understand bullet drop at different angles and distances for different calibers, then you can make an informed decision.

    :)
     
  18. blackops

    blackops Member

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    I was speaking of shots inside 400yds and I mentioned that in my thread. I don't plan on taking hunting shots with my 270 at 1k. And by the way they aren't using a 300 win mag in the Panshir Valley. Its the 338, 408, 416, and 50bmg.

    .

    HAHAHA Rub it in my face a little more please! lol
     
  19. ~z

    ~z Member

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    Ops, I’m not quite sure why you are showing such disrespect to the person who is providing you with the most (and most thorough) information on the topic.
    In your original post you did not mention hunting, you mentioned "target" but not what that target was.
    Sometimes these things (physics problems) become a bit more obvious once you extend distances so as to magnify errors. Conversely, yes you will see these discrepancies with your .270 at 400yds shooting on an incline. Possibly more depending on the angle. Angles have a way of flattening themselves out with distance, rarely will you find a place to make a 1K shot at an angle 45 but a 400 yd shot at that angle is a whole lot easier to come across.
    ~z
     
  20. MCMXI

    MCMXI Member

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    blackops, I was hoping that my examples would be helpful but I guess not. I won't waste any more of your time. Maybe I was thinking of British soldiers in Afghanistan using an AI in .300 Win Mag. Regardless, it was for illustrative purposes and was a waste of my time too. I won't make that mistake again.

    :)
     
  21. PT1911

    PT1911 Member

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    I was being a bit of a smartass with a point with that statement...

    simply put.. if you were able to zero your weapon at the peak of your bullets trajectory, before bullet drop is even part of the conversation, then you eliminate the conversation..

    though... theoretically, I guess under certain circumstances the angle of the shot could also effect the bullet rise that takes place immediately after the bullet leaves the muzzel...:D
    By saying "for all practical purposes" I was limiting my response to shots that the average person is likely to take. (ie 1000 yd shots from the top of a mountain)

    I feel that the majority of hobbie shooters are too caught up in the advice they receive on the internet and magazines.. too worried about the barometric pressure, temp., wind, humidity, lighting and now the angle of the shot having an affect on their POA v POI. The fact is, if you spend the money on a quality gun and the time shooting it, it is likely the gun will still shoot better than you.
    (by you I mean even well above average shooters.)
     
  22. blackops

    blackops Member

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    1858, Not trying to argue. I just thought the
    comment was referring towards me. No worries. Your help was useful! Thank you for taking time to help me out. Still they aren't using 300 Win Mag :neener:
     
  23. ~z

    ~z Member

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    PT, “the bullet rise that takes place immediately after the bullet leaves the muzzle”
    Unless you are shooting at an upward angle, the bullet does not rise immediately after leaving the muzzle, it begins to fall.

    Ops, ignorant is not a bad word, it just means unknowing, you were unknowing (ignorant) so you asked the question.
    ~z
     
  24. PT1911

    PT1911 Member

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    sorry to argue, but are you serious? Explain how a gun can be zeroed at a distance and shoot both low and high at closer distances than its zero if the bullet is going straight down after leaving the barrel.

    zero a gun at 100 yards and see where the bullet is hitting at 10, 25, 35, 50...etc... the bullets trajectory is an arch after leaving the barrel..

    If the bullet went straight down after leaving the barrel then a zero at 100 yards would be high from 1 to 99 yards. Try the above experiment and you will find that is most definitely not the case..
     
  25. Float Pilot

    Float Pilot Member

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    Actually he is correct, although he did not say it clearly.

    IF, you had a rifle barrel perfectly level. The bullets path drops from the line-of-sight and continues to drop until it hits the earth. In fact if you fired a bullet on the moon and droped another bullet at the exact same time they would both hit the ground at the same time. On earth, the resistance of the air makes a little difference.
    If, as in your example the rifle is zeroed for 100 yards, the barrel is not perfectly level. In your example the barrel is slightly elevated to compensate for gravity. Thus the arcing trajectory.

    Of course if you fire a bullet fast enough that it falls at the same rate that the curve of the earth drops away, then you have orbital velocity.
     
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