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As the world turns fact or fiction?

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

  1. KevinR

    KevinR Well-Known Member

    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

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

    Quentin Well-Known Member

    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 Well-Known Member

    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.

  5. Quentin

    Quentin Well-Known Member

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

    KevinR Well-Known Member

    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 Well-Known Member

    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 Well-Known Member

    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.

  9. dagger dog

    dagger dog Well-Known Member


    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 Well-Known Member

    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

  12. Oic0

    Oic0 Well-Known Member

    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 Well-Known Member

    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

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

    Slamfire Well-Known Member

    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 Well-Known Member

    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 Well-Known Member

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

    Uncle Mike Well-Known Member

    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 Well-Known Member

    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.

    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 Well-Known Member

    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


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