Long Distance Shooting Calculations

Discussion in 'Competition Shooting Forum' started by Conman, Jun 22, 2017.

  1. The_Rifleman

    The_Rifleman Well-Known Member

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    You are getting the effects mixed-up.

    There are many effects that you must take into account, and some can somewhat offset another; as when using a left hand twist in the northern hemisphere.

    Bypassing conventional drop and windage calculations, lets start with...
    Spin Drift, (Gyroscopic Drift.) A right hand twist, will cause the bullet to drift to the right; anywhere on the earth, and while shooting in any direction.

    Coriolis Effect works off of the earths rotation, and is a windage-wise effect; in the northern hemisphere, it drifts right, and the southern, left. The poles have the most effect the equator has less. No mater which direction you shoot, you get the same amount of effect.

    Eötvös Effect is the height-wise effect that works with the centrifugal force of the earth's spin. It is greatest at the equator, and nonexistent at the poles. The shooting direction dictates how much effect. Shooting east and west has the most effect, and the effect diminishes as the direction aims north or south. East hits higher, west hits lower.

    http://aegisacademy.com/external-ballistics-part-iv-deviation-gyroscopic-drift-and-wind-deflection/

    https://loadoutroom.com/thearmsguide/external-ballistics-the-coriolis-effect-6-theory-section/
     
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  2. Krong of Belsnarf

    Krong of Belsnarf Member

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    I was under the impression that The OP was asking about how the rotation of the earth affected bullet flight. I limited my reply to the Coriolis Effect. Things in the NH do tend to veer to the right as you said. I disagree with you and with the loadoutroom fellow that the angle makes no difference. If you shoot from one place on the earth that is going 1,000 miles an hour to another place that is going 1,000 miles per hour, the bullet will not veer due to Coriolis Effect. If you shoot at an object to the due south of you (in NH), then you are not going as fast as the target and the bullet will hit to the west of the target. The difference in speed of the surface of the earth between the point of firing the bullet and the point of bullet impact is what causes the effect.

    When wing shooting at a moving bird, you shoot where the bird is going to be when the shot gets there and not where the bird is when you fire the gun. If the bird is passing at right angles, the lead has to be greater than if the bird is quartering away. A bird going straight away from you requires no lead.
     
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  3. The_Rifleman

    The_Rifleman Well-Known Member

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    Then you disagree with everyone.
    http://www.appliedballisticsllc.com/Articles/ABDOC108_GyroscopicAndCoriolis.pdf
    "The Horizontal component depends on your latitude, which is how far you are above or below the equator. Maximum horizontal effect is at the poles, zero at the equator. The horizontal component doesn't depend on which direction you shoot. Typical horizontal Coriolis drift for a small arms trajectory fired near 45 degrees North Latitude is about 2.5 - 3.0 inches to the right at 1000 yards."

    https://scijinks.gov/coriolis/
    This is why hurricanes continually spin.


    https://en.wikipedia.org/wiki/External_ballistics#Coriolis_drift
    "Horizontal effect
    Viewed from a non-rotating reference frame (i.e. not one rotating with the Earth) and ignoring the forces of gravity and air resistance, a projectile moves in a straight line. When viewed from a reference frame fixed with respect to the Earth, that straight trajectory appears to curve sideways. The direction of this horizontal curvature is to the right in the northern hemisphere and to the left in the southern hemisphere, and does not depend on the azimuth of the shot. The curvature is largest at the poles and zero at the equator.[63]"

    We are shooting on a sphere, not a 2 dimensional disk.
     
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  4. gdmoody

    gdmoody Moderator Supporting Member

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    Lord have mercy, no wonder I keep missing those 200 yard shots, I never took the rotation of the earth into consideration!!
     
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  5. The_Rifleman

    The_Rifleman Well-Known Member

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    That explains it much better than I can, and demonstrates it.
     
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  6. carver

    carver Moderator Supporting Member

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    Kentucky windage works for me out to 500 yards, after that it's just a SWAG!
     
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  7. drymag

    drymag Well-Known Member

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    Try the redneck method: Take a few pounds of flour with you and sprinkle the ground. Then fire for effect and watch the plumes and walk it in.
     
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  8. The_Rifleman

    The_Rifleman Well-Known Member

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    Like I alluded to; the spin drift of a left handed twist, shot in the northern hemisphere can entirely negate the coriolis effect. So you must take that into consideration.

    The Eötvös Effect is also attributed to the earth's rotation.
    So all 3 of these effects can be a factor to the OP's question.
     
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  9. Krong of Belsnarf

    Krong of Belsnarf Member

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    I admit defeat and appreciate the educational experience. Since we are on a rotating sphere, our motion anywhere except on the equator has both a vertical and a horizontal component. The motion at the equator just has a vertical component since we would be perpendicular to the axis of rotation.

    Krong at the equator 43 years ago. That must have been the one time when I did not veer off to the right or left.
    59.jpg
     
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  10. UncleFudd

    UncleFudd Well-Known Member

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    I guess I'm too old to learn all these new tricks. I have been shooting prairies dogs near our ranch in SW Wyo for more than 50 yrs. Used only a scope and 22-250 Rem 700 rifle. We usually don't shoot at em unless they are 250 yds or more out to about 500 yds. But in the constant Wyo wind you learn to use Kentucky windage very quickly and very well.
    Last Feb I had a chance to shoot the 1,000 yd LR shoot at the SW nationals. We had a breeze from lt to rt all day and it stayed fairly consistent that day. After shooting my "sighters" at each station, I just used the windage and shot clean at each distance out to 600 before dropping a single 10.
    I finished with a 194/200 4X at the 1,000 yd still just using the windage.
    Some of the better more experienced shooters had all kinds of gadgets on and off their rifles to tell the exact windage and even to null the sonic vibrations at the muzzles of their rifles along with some really strange looking and beautiful stocks and other acutrements. Really interesting and wild stuff to this old cowboy, but I still had a ball the who;le time.

    UF
     
  11. ms6852

    ms6852 Well-Known Member

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    That is the philosophy all of my four younger brothers use. Zero at 100 and aim higher at longer distances regardless of caliber. How they manage to put venison in the freezer is always beyond my understanding, but I do know that always have at least 2 boxes of ammo with them just in case.:D
     
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  12. carver

    carver Moderator Supporting Member

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    If I knew that I was going to be shooting at 500 yards, my gun wouldn't be sighted in for 100 yards. Deer hunting down here is a little bit more up close, and personal. A 100 yard shot is a long shot in our experience! Usually inside 50 yards. The only reason you might need a second shot, is because your bullet hit some brush of some sort, and turned your bullet before it go to it's target. This is one of the biggest reasons you see a lot of shotgun deer hunters down here. Shotguns work well with slugs, or buck shot out to 50 yards. And some of us will stretch it out to 75 yards with either slugs, or 00 Buck.
     
  13. ms6852

    ms6852 Well-Known Member

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    The closest I have ever shot a deer was about 80 yards or less. It was at a full gallop coming straight at me when it saw me it veered to my right I dropped to my knee. I had plenty of time to track it a couple of times so I could time its pace and give it a lead. But mostly here in west Texas where we hunt our shots are at a minimum of 150 to 200+ yards. For Aoudad it stretches a littler farther. I refuse to walk those mountains in Fort Davis.
     
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