Spin drift and Coriolis at 1000+

Discussion in 'Extreme Long Range Hunting & Shooting (ELR)' started by sdowney, Oct 8, 2012.

  1. sdowney

    sdowney Well-Known Member

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    Assuming most of us are shooting in the northern hemisphere and using right hand twist barrels, how do you guys account for the above? From my research, I'm seeing anywhere from a .5 to 1.25 MOA drift right at 1000 yards. If you zero for say 300, do you add some left MOA to account for the longer ranges knowing the being an inch or two to the left at 300 probably isn't going to change much.

    I'm about to pick up my new custom 338 Norma Mag and was just curious about the effects of spin and coriolis at 1000-1500 yards. Thanks for your widsom.
     
  2. Broz

    Broz Well-Known Member

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    I use "Shooter" and now also Bryan Litz new Applied Ballistics programs on my Droid phone. Both of these programs will give you corrections for spin drift and corriolis tuned to your rifles ballistics and from your shooting location.

    I leave SD checked on as part of every shooting solution. But I only employ the coriolis to be part of shots beyond 1200 yards as the effects are usually small before that.
    Jeff
     

  3. sdowney

    sdowney Well-Known Member

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    Cool. I've heard of shooter. Is Bryan's program available from the google play store for droids?
     
  4. Broz

    Broz Well-Known Member

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    I purchased mine from his Applied Ballistics site, and it is the most advanced program I have found to use.

    Jeff
     
  5. sdowney

    sdowney Well-Known Member

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    I feel honored to have such a LR master answer my questions. One last: what is your gut feel for my .338 norma shooting a 300 gr OTM at 1000? Would you guess 6"? 10"? 15"

    Scott
     
  6. Broz

    Broz Well-Known Member

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    Scott I would not go that far. I just shoot a lot and like talkin shooting and hunting.

    Not sure I understand the question. Are you asking about the spin drift effect?

    Jeff
     
  7. sdowney

    sdowney Well-Known Member

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    My bad. How much will my bullet move right at 1000 yards for my .338 NM (adding SD and corioilis)? Just your gut feel.

    And, you are one of the most revered guys on this site. Thanks for all your inputs and knowledge sharing. Lots of time on your part. Not unappreciated!!
     
  8. Broz

    Broz Well-Known Member

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    Thanks for the kind words and you are more than welcome.

    Lets leave coriolis out of this as it is dependent on the direction of the shot (azmuth) and also involves latitude. Besides I feel its effect is smaller than we could probably detect at only 1000 yards.

    So for your right twist 338 with a 300 gr OTM at 1000 yards. 1/2 moa or 5" would be a pretty safe distance to dial left for correction.

    Jeff
     
  9. Joe King

    Joe King Well-Known Member

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    Scott I would buy Bryan's book Applied Ballistics, his ballistics program comes with it. I think you would find it invaluable.

    Products
     
  10. sdowney

    sdowney Well-Known Member

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    How profound.
     
  11. Broz

    Broz Well-Known Member

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    Is that the mobile app that comes with the book or a PC program? That is a great deal either way.

    Jeff
     
  12. 270 MKV

    270 MKV Well-Known Member

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    Can someone verify the following??

    Matrix 165 VLD

    MV: 2850 FPS

    Barrel Twist: 1-9

    Range: 1000 yards


    Projected spin drift: 6.38 inches
     
  13. submoa

    submoa Well-Known Member

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    Doesn't spin drift go up and to the right? And isn't the Coriolis affect the affect of the earth rotation on the POI? hence shooting east POI is lower and west its higher or do I have this backwards?
     
  14. LR3

    LR3 Well-Known Member

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    Submoa, the way I think of it is that if a truck was coming at you or by you from the rising sun what would I do? Or the sun, which is really the effect. Shooting east, the sun is coming at you at high speed and hence bullet fall is less, shooting west it's going away, hence needs to go further, hence drops more. Similarly, shooting north or south the earth will have rotated westward, hence the bullet will be to the right of target shooting north but left if shooting south. At 1000 yds for me shooting north that is aboutb3" and add that to spindrift. At 2000 yds my spindrift is 1.4 moa. So, depends on the direction and where you are how big the effect is but as Broz said, at 1000 yds not huge. I ve tried to setup my scopes with a slight dip to the right so when level it cants to the left (1 minute on a watch face) and except for one rifle I don't seem to have gotten it right and then only at 1000yds. There was a discussion about this about a year ago. Bryans book is excellent in explaining this.