spin drift & Coriolis effect

Discussion in 'Long Range Hunting & Shooting' started by rem, Mar 16, 2011.

  1. rem

    rem Well-Known Member

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  2. WyoElk2Hunt

    WyoElk2Hunt Well-Known Member

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    There was an article on TV about the 30/40 Craig rifle and the flip up sight for long range shooting that it had a wire in the sight to account for the spin drift as you elavated the sight. This was during the Spanish American War so they knew about spin drivt way back then especially with heavy round bullets. Don't know about faster bc bullets.
     

  3. tresmon

    tresmon Well-Known Member

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    I teach it in detail in my LONG Range shooting Seminar.

    I disagree with the blog guys statement that he feels it doesn't matter if you not going to be making 1500y cold bore shots.

    For my long range rifle Coriolis is worth 3" right at 1000 yds, a range I shoot at frequently.
    Coriolis is worth "about" (too lazy to look up the exact figure right now) another 3" right.

    So if I guess what the wind is going to do to my bullet @ 1000 yards perfectly ("perfectly?" basically not possible) set my sights perfectly for 1000, break the shot perfectly, the ammo & velocity is perfect- I'm still going to miss the mark by 6" due to Spin D and Cori alone.

    Now Me and every other HONEST down to earth shooter will admit they need all the help they can get for long range cold bore shots. We estimate the wind but will be a little off. Our MV varies shot to shot. All these minopr unavoidable erros stack up in long range shots so yes you had better account for Cori & spin D. We need all the help we can get at long range.

    As a side note: if we inhabitants of the northern hemisphere were smart we'd shoot barrels with left hand twist rifling. This would pit spin drift and cori against each other and mostly cancel the two out!

    Come to class!
    http://www.longrangehunting.com/for...nge-shooting-class-nashville-tn-3-19-a-68987/
     
  4. BlackSS

    BlackSS Well-Known Member

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  5. tresmon

    tresmon Well-Known Member

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    You can order a LH twist bore from about any custom barrel manufacturer...

    My guess is to our use of RH bores is that we just live in a RH world. I don't have a technical answer nor do I know if their is one...

    However for trivia, the ol' .303 british round & rifles were LH bores...
     
  6. rscott5028

    rscott5028 Well-Known Member

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    Stupid questions:

    (A) Wouldn't it depend on whether you are shooting north or south as to whether coriolis would take your bullet left or right?

    (B) Why did the US military abondon their experimentation with left hand vs right hand twist?
     
  7. rem

    rem Well-Known Member

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    it seems that the only way to deal with this is to figure out what your bullet does. I can't imagine 2.5" at 1000 really maters. if you can shoot 2.5" groups @1000 then it seems it would matter. 2.5" groups win bench rest compations. the smallest temperature change will make the bullet miss at 1000 yards
     
  8. tresmon

    tresmon Well-Known Member

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    Rem,

    2.5" does matter @ 1000 yards. You make the same mistake/assumption everyone else does.


    Let's say I'm making a 1000 yard shot at a white tail deer. I'm shooting at a 10, maybe 12 inch vital zone.

    I guess the wind and break the shot.

    Well, I pulled the shot to the right 1". That's a teeny pull if it only effects the 1000 yard shot an inch. But now my bullet is going to land tin the right quadrant of the 10 inch kills zone, matter of fact 1 inch right of center, but still 4 " from the right edge of the kill zone. So we're good.

    I thought the crosswind was value x and would drift my bullet 8" and I compensated for 8". However the wind is actually y which is a bit more and will actually push my bullet an additional 4" that I had not anticipated.

    So my 1" right pulled shot, plus my extra, unaccounted 4" of drift have now added together for 5" right error and my bullet is going to land in the very extreme right edge of the kill zone. So I got lucky, I'm still barely on the VERY edge of the kills zone.

    OPPS! I forgot to add "those three little inches" of coriolis effect. Crap

    1" pull error + 4" wind error, plus 3" coriolis =8" and now I've hit the animal well outside the vital zone.

    I arrest my case. As I said, every "little" thing counts in long range shooting and the long range shooter needs all the help he can get as well as he needs to split every hair on the figuring & prepping end of the long range shot.

    The same is said for long range competition shooting. A teeny little disregarded inch can make the difference of a 10 ring hit or a 9 ring hit and cost you the match.

    Same for a tactical match shooting at steel targets. That little "insignificant 2.5 inches" can mean the difference between hitting the edge of the steel plate and winning or missing the edge by an inch and blowing the match.

    The further the shot, the more heavily little things need to be scrutinized and factored in.
     
    Last edited: Mar 16, 2011
  9. load

    load Well-Known Member

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    no. shooting north and south east or west you always have a impact right component. however shooting east and west (and varying degrees )you also have a vertical component. shooting west you'll hit low, shooting east you'll hit high.
    at 45 degrees north lat the following will get you close
    1/4 moa @1000 yrds
    1/2 moa @1500 yrds
    3/4 moa @1760 yrds

    for varing degrees of east and west divide into full, 3/4, half, and 1/4 values. simular to the way you divide wind values.
    gun)
     
  10. load

    load Well-Known Member

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    no. shooting north and south east or west you always have a impact right component. however shooting east and west (and varying degrees )you also have a vertical component. shooting west you'll hit low, shooting east you'll hit high.
    at 45 degrees north lat the following will get you close
    1/4 moa @1000 yrds
    1/2 moa @1500 yrds
    3/4 moa @1760 yrds

    for varing degrees of east and west divide into full, 3/4, half, and 1/4 values. simular to the way you divide wind values.
    please keep in mind also that wind plays a vertical component also.
    blowing left to right your bullet will drop. right to left the bullet will rise. this is also an effect of the spinning bullet
     
  11. rem

    rem Well-Known Member

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    I understand your point, but lets say you account for all of the variables on your 1000 yard whitetail shot. if your gun shoots 1MOA at 1000 yards you are still very likely to miss the vital area. not to mention 1mph of wind will drift your bullet at least 4"(depending on your caliber fps and BC). I shoot at distances at targets before I ever shoot at an animal at that range. If i have 1.25 MOA worth of drift at 1000 between spin and Coriolis Effect I know exactly what it is because I have shot at that range many times before I will take the shot.
     
  12. RDM416

    RDM416 Well-Known Member

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    Rem,

    Tresmon is exactly right, all those errors ADD up! To simply say you cannot shoot better that that is to miss the point..... and the target, (pun intended):D

    At 1000 yards the the spin drift on my favorite .338 load is around 5". I can reliably shoot 5" groups at 1000 sometimes better. I certainly don't want those groups to be 5" to the right at 1000 yards anymore than I would want them to be 5" to the right at 100 yards.

    I don't want to start any arguments here, so I will say this is my OPINION..... If you are going to be shooting at game animals your rifle should be able to shoot a group less than the kill zone diameter of the the animal you are shooting at. For example: Lets say a whitetail has a kill zone of 10" dia. If your rifle is capable of shooting only 1 moa, that is the same as the entire kill zone..... no margin for error. In my opinion a 1 moa rifle should be used to only 700 or 800 yards. In my "opinion" a rifle used on game animals at 1000 yards should be capable of shooting 1/2 to 1/4 moa. This allows for some SMALL amount of error in aiming, spin drift, coriolis, velocity, temperature, humidity, elevation, angle, and of course that pesky wind.

    Unlike wind, spin drift is a very predictable value so why not go ahead and compensate for it? Coriolis effect is a little more difficult to compensate for since it does change depending on the direction of your shot. However, the proliferation of "smart phone" based ballistic programs make this easier than ever since the phones have a gps in them.

    Tresmon, Will you be having any additional classes later this spring/summer? I am only about 6 hours from you in AR and my wife has family in Nashville. I would love to attend your class this time, but I have training to go to for 4-H shooting sports. Keep us updated if you have any more classes.
     
  13. RDM416

    RDM416 Well-Known Member

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    Rem,

    Tresmon is exactly right, all those errors ADD up! To simply say you cannot shoot better that that is to miss the point..... and the target, (pun intended):D

    At 1000 yards the the spin drift on my favorite .338 load is around 5". I can reliably shoot 5" groups at 1000 sometimes better. I certainly don't want those groups to be 5" to the right at 1000 yards anymore than I would want them to be 5" to the right at 100 yards.

    Unlike wind, spin drift is a very predictable value so why not go ahead and compensate for it? Coriolis effect is a little more difficult to compensate for since it does change depending on the direction of your shot. However, the proliferation of "smart phone" based ballistic programs make this easier than ever since the phones have a gps in them.

    Tresmon, Will you be having any additional classes later this spring/summer? I am only about 6 hours from you in AR and my wife has family in Nashville. I would love to attend your class this time, but I have training to go to for 4-H shooting sports. Keep us updated if you have any more classes.
     
  14. Bravo 4

    Bravo 4 Well-Known Member

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    So was this supposed to say you add 3" right for Spin Drift and another 3" right for Coriolis? If so, I hate to tell you this but you cannot just put a number on Coriolis like you can Spin Drift because it is never gonna be constant...unless you are shooting at the same range (and I don't mean range as in distance, I mean range as in Firing Range/shooting spot).


    Yes, it does depend on the direction you are shooting in conjuntion to true north/south. It will not always make your bullet drift right like spin drift from a right hand twist barrel. I believe the the poster below didn't quite catch onto your question.