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As the world turns fact or fiction?

Discussion in 'Rifle Country' started by KevinR, Mar 21, 2010.

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  1. KevinR

    KevinR Member

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    I am sure that all of us have seen and herd in the movies that the rotation of the earth needs to be taken into account when shooting long distances.

    My question is how much does the earth actually turn at 500 yds or even 1000yds. Is this even worth considering when a bullet may only be in flight 2, 5 or even 10 seconds. Or is this as I suspect, just bullskatoligy?
     
  2. Art Eatman

    Art Eatman Administrator Staff Member

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    Aside from 16" naval shells and rockets, figure that it's "just bullskatoligy".
     
  3. Quentin

    Quentin Member

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    Well the circumference of the Earth at the equator is about 25,000 miles and one day (rotation) is 24 hours so a point on the equator is moving about 1,000 miles an hour.

    Thing is your gun and the target are lockstep, moving the same speed so I'd say forget about it and worry about what really matters like your shooting technique, breathing, ammo ballistics, the rifle/sights and weather conditions.
     
  4. dagger dog

    dagger dog Member

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    The earth turns east at approx 750 miles per hour, a British small arm committe in 1886 discovered a projectile would deviate 6" to the right (northen hemisphere, see Coriolis effect.) in 1,000 yds. Maximum drift occurs when fired toward the southwest, this effect is coupled with spindrift from the rifiling twist.

    from UNDERSTANDING FIREARM BALLISTICS By Robert A Rinker
     
  5. Quentin

    Quentin Member

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    Methinks Robert A Rinker might need to read another book on UNDERSTANDING FIREARM BALLISTICS :)
     
  6. KevinR

    KevinR Member

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    If in fact Mr Rinker knows what he is talking about and I suspect that he does, all the rifle ranges in my area are facing the wrong direction. The state range is the worst, it faces directly south west. :barf: Just out of curiosity, what direction do other ranges of other members face?
     
  7. Casefull

    Casefull Member

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    Not that it matters a lot but the earth is always spinning at a constant velocity. If your rifle is sighted in at 1,000 yds(ha!) then you have already taken the earths rotation into account just like you have accounted for gravity...I suppose east west shots would be affected less than north south...I give up.
     
  8. R.W.Dale

    R.W.Dale Member

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    I may not be a real sniper or play one on TV but my hand head ballistic computer does have an output for Coriolis effect.

    http://www.classzone.com/books/earth_science/terc/content/visualizations/es1904/es1904page01.cfm
     
  9. dagger dog

    dagger dog Member

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    Kevin,

    Knob Creek Range, out side Louisville KY is where I shoot the most, and it lies somewhat southeast, and it is an old Ft. Knox military range.
     
  10. Zerodefect

    Zerodefect Member

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    Since we are moving at the same speed as the earth it shouldn't matter. Rockets are leaving the Earth so it matters. I think if it made our rounds off 6" at 1000yard, we would have noticed by now.

    I highly doubt Naval cannons account for the earths rotation. Do they really?
     
  11. MythBuster

    MythBuster member

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  12. Oic0

    Oic0 Member

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    Unless I am mistaken perhaps land on the equator is moving faster than land closer to the poles, in that case it would only make a difference if firing longitudinally and over a distance long enough for it to matter?

    Get what I mean? the bullet is moving the same speed as you with the earth spinning motion, fire it somewhere far away on a different plane of the axis and the bullet is still going whatever speed it was when you fired it but the objects on the ground where it ends up are moving at a different speed.
     
  13. Tirod

    Tirod Member

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    Look up the history of the German railroad gun Big Bertha. They used it to shoot at Paris ( military targets around the outliers.) Problem was the first time they missed the impact zone selected by a significant margin. Forward observers were reporting the amount of offset and the German gunners weren't happy with their calculations - until they took into account the flight time of the projectile. What had happened was that "Paris had moved!"

    Once the rotational speed of the earth is factored in, then impact is on target. As said, it's a big gun problem. At the rifle level, I doubt shooting at 1000m needs much correction.

    Nonetheless, I wouldn't be surprised to find an app for that . . .
     
  14. taliv

    taliv Moderator

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    there is an app for it. in fact, even the KAC bulletflight software on my iphone takes it into account
     
  15. Slamfire

    Slamfire Member

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    I have never noticed the earth's rotation effecting my bullets at 500 yards or 1000 yards.

    I did notice that cross winds made one heck of a difference on point of impact versus point of aim. :cuss:

    Now, if I was shooting at Heavy Cruisers 26 miles away, I suspect the movement of the earth under the projectile might make a difference.
     
  16. aka108

    aka108 Member

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    It really doesn't matter. Anyone with any grey matter between their ears knows that the world is flat.
     
  17. R.W.Dale

    R.W.Dale Member

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    as does my "ballistic'" app
     
  18. Uncle Mike

    Uncle Mike Member

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    The Coriolis Effect does indeed affect projectile flight. At the distances we normally shoot handheld firearms the effect is so small it is not a factor...but, in any event, it still does exist and affect projectiles in flight.
     
  19. T.A.Sharps

    T.A.Sharps Member

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    Its True

    The Earths rotating and moving under the bullet is true.

    Yes the bullet was moving at the same speed as the Earth, but not after it left the barrel.

    However,
    It is an effect that only matters to long range shooters, that are changing regions of the world often. Something not likely for any one here to be dealing with, and if anyone is, they certainly already know about the physics of this.

    The fix is to simply re-zero your rifle, the effect is a constant, always the same for where you are at in the world.

    You would have more adjustments more often to correct that actually change all the time like temperature change, differences in batches of ammo, or air density.
     
  20. MCMXI

    MCMXI Member

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    From Wikipedia ....

    The Coriolis effect is the behavior added by the Coriolis acceleration. The formula implies that the Coriolis acceleration is perpendicular both to the direction of the velocity of the moving mass and to the frame's rotation axis. So in particular:

    * if the velocity is parallel to the rotation axis, the Coriolis acceleration is zero.
    * if the velocity is straight inward to the axis, the acceleration is in the direction of local rotation.
    * if the velocity is straight outward from the axis, the acceleration is against the direction of local rotation.
    * if the velocity is in the direction of local rotation, the acceleration is outward from the axis.
    * if the velocity is against the direction of local rotation, the acceleration is inward to the axis.

    So in other words, make sure to shoot North or South so that you don't have to worry about it. The CF is at a maximum shooting East or West!! :D If your bullet has as a crappy BC, you may want to consider shooting East since your bullet will drop less!! :D

    :)
     
  21. BruceB

    BruceB Member

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    Take a hard look at the rear (barrel) sight on a M1903 Springfield.

    The "rails" that guide and support the notch assembly when the sight leaf is raised are noticeably tapered, with the left side getting narrower as the range setting increases, and the right side getting progressively wider. This of course moves the sight element further and further to the left as the range setting increases. Does anyone here think that this was by accident? The arsenals knew full well that there is a ballistic factor that changes the impact point to the right as range increases.

    Whether the change is caused by atmospheric effects or the Coriolis phenomenon, the fact remains that there IS a change. It's only obvious at extreme range, but it is there. To see a pretty good picture of the '03 sight leaf, go to www.auctionarms.com and search for item #9575909, and the tapered rails are VERY obvious.

    According to my information, the British .303 rifles were rifled with a left-hand twist to compensate for the rotation of the Earth....in the NORTHERN hemisphere.
     
    Last edited: Mar 21, 2010
  22. Dimis

    Dimis Member

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    i cants say anything for sure as im not a scientist a ballistition or anything more than a local rural boy playing with his toys but i believe the rotation of the earth only comes into play with extreme long range shots well beyond 1000 yards
    like shots at 1 mile or beyond so for most of us it wouldnt effect us enough to notice or need to care
    unless we are absolutly obsessed with absolute perfect accuracy which im almost possative is completly unatainable its a moot point

    so unless you have a big boy rifle in a caliber that reaches 2000 yards and beyond its nothing to be concerned about

    YMMV
     
  23. Hud

    Hud Member

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    It does have an effect, but...

    From Canadian Manual:
    B-GL-306-006/FP-001
    FIELD ARTILLERY
    VOLUME 6
    BALLISTICS AND AMMUNITION

    “In manual computations, rotational effects are not applied in Canadian gunnery procedures at ranges under 15000 metres, as the additional accuracy achieved does not justify the time expended.”

    So, if they don't worry about it with artillery under 15,000 meters (that's 9 1/3 miles folks), I doubt if we need to be concerned with any calibers that we shoot at any range.
     
    Last edited: Mar 21, 2010
  24. taliv

    taliv Moderator

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    1) "they" == canadiens

    2) sure, the additional accuracy might not justify an extra 20 minutes with a slide rule
    but if it takes an iphone a second and a half to calculate it, why wouldn't you want the additional accuracy?
     
  25. Hud

    Hud Member

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    Well, I really don’t feel a need for it, but if it works for you, I’m sure the iPhone app has it all over those stone-age Canadians.:)
     
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