Wind Drift

Discussion in 'Long Range Hunting & Shooting' started by bjlooper, May 31, 2006.

  1. bjlooper

    bjlooper Well-Known Member

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    I have read more than a few post on this fourm as well as others. That imply that by going to a heaver bullet or to a larger caliber that you will get less wind drift.
    Am I mistaken I thought that the weight or the caliber of the bullet had nothing to do with wind drift. The only thing that matters is time of flight. Which means that velocity and balistic coefficient, are the main factors effecting wind drift.
    example of this is if you have two bullets Shoot at 3000 fps and are traveling in a 90 degree ten mph cross wind. bullet A is .243 cal 80 gr with a BC of .534 and Bullet B is a .243 cal 105 gr with a BC of .534. They will have the same wind drift and the same drop and the same time of flight at any given range.

    So if I'm wrong will some one please teach me what is correct.

    DR B
     
  2. bailey1474

    bailey1474 <strong>SPONSOR</strong>

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    [ QUOTE ]
    two bullets Shoot at 3000 fps and are traveling in a 90 degree ten mph cross wind. bullet A is .243 cal 80 gr with a BC of .534 and Bullet B is a .243 cal 105 gr with a BC of .534. They will have the same wind drift and the same drop and the same time of flight at any given range.

    [/ QUOTE ]

    Your example is 100% correct. It's just that in the real world, as bullet weight increases, so does bc. For example that 80 gr bullet you listed will really hava bc of around .350-.375 where that 105 (depending on manufacturer) will have a bc of .500 to .550 +.

    That is why going heavier usually gives you less drift /ubbthreads/images/graemlins/wink.gif.
     

  3. arthurj

    arthurj Well-Known Member

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    Yes, that's right. Higher BC and velocity gives the bullet a shorter time of flight at a given distance. Bullet weight does not matter, like you said. Bullets of different weights, with the same bc and velocity will have the same wind drift and time of flight. Less time in the air, = less time for gravity and wind to affect the bullet.
     
  4. abinok

    abinok Writers Guild

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    Technically, its not the time of flight thats the issue in wind drift, its the differance between the time of flight, and the time of flight that would have occured if the bullet had continued at muzzle velocity all the way to the target. Higher BC (heavier) virtually ALWAYS have longer time of flight, but will have less wind drift.
     
  5. bjlooper

    bjlooper Well-Known Member

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    Bill bailey
    My bad Bullet A is .223 80 gr berger VLD not a .243 the BC is correct for the .223 bullet
    Dr B
     
  6. bjlooper

    bjlooper Well-Known Member

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    Abnoik
    Time of flight is the amount of time that the wind has to act on the bullet. When a object traveles thruogh the Atmosphere the weight has no bering of how fast it drops of how far it drifts.
    Dr B
     
  7. abinok

    abinok Writers Guild

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    I agree that weight has no direct bearing on path or wind drift, however, as I mentioned above, its not time of flight that determines wind drift, its the differance between the time of flight, and the time of flight that would have occured if the bullet had continued at muzzle velocity all the way to the target.

    Weight only affects the flight of the projectile by its relationship to the ballistic coefficent. BC is sectional density multiplied by form factor. Sectional density is determined by weight and caliber. If the form (shape of the bullet) is held constant, increases in weight raises the sectional density, which reises the BC. Again, only BC and velocity affect wind drift and path. Weight, while a factor in both of these values, is not a direct contribuitor.

    Again, Higher BC bullets in the same cartridge, which usually weigh more, will ahve a longer time of flight than lighter bullets, but still have less wind drift.

    To put it yet another way, the amount of wind deflection a bullet experences in flight is not directly proportional to the amount of time it is in the air, but rather the differance mentioned above. It is for this reason that vind velocity near the muzzle will result in more deflection than the same wind at a longer range.
     
  8. bailey1474

    bailey1474 <strong>SPONSOR</strong>

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    [ QUOTE ]
    Abnoik
    Time of flight is the amount of time that the wind has to act on the bullet. When a object traveles thruogh the Atmosphere the weight has no bering of how fast it drops of how far it drifts.
    Dr B

    [/ QUOTE ]

    True, but in the real world, the heavy for caliber bullets will have a much higher bc than the light for caliber bullets. This translates into more tof for the heavier, higher bc bullet but despite this, the heavier higher bc bullet will have less wind drift.
     
  9. abinok

    abinok Writers Guild

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    BJ,
    "smacks forehead repeatidly"
    I hate trying to explain stuff as technical as this over the net... because its so hard to articulate!
    as an add on...
    that bullet... ive got chrony generated BC data 0-100yds, and 0-400yds that are pointing towards the .65-.68 range. Im interested to see how that compares to the generated figures you recieved, and the drop tables youve been using. Email me when you get the chance.
     
  10. goodgrouper

    goodgrouper Well-Known Member

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    [ QUOTE ]
    as bullet weight increases, so does bc.

    [/ QUOTE ]


    This is not always so. Ballistic coefficient is derived from the coefficient of form which means that the bullet's shape is the important thing and weight is indirectly related. Usually, as you add weight to a bullet it gets longer. But the shape must still be aerodynamic or the added weight is counterproductive because velocity will be reduced and time of flight will increase. If weight is added to a bullet and the shape remains the same, then the bc will go up because the bullet is getting longer while the shape is staying the same.

    Take for instance the 160 grain 6.5 mm round nose Hornady flat base. BC=pathetic (I believe it is in the .3's) and then look at the 140 grain Berger VLD with it's bc of .627. Almost double the bc with 20 grains less weight. Why? The coefficient of form or the shape is much more aerodynamic on the Berger.

    I realize you probably already know this, but it helps to clarify the exact derivitive of the definition so as to not confuse the original poster. /ubbthreads/images/graemlins/wink.gif
     
  11. abinok

    abinok Writers Guild

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    155gr SMK compared to the 142 SMK is a great example as well. Did I not articulate that very well above? gotta be careful about how I say this kind of stuff or Iconfuse everybody and myself! /ubbthreads/images/graemlins/smile.gif
     
  12. bjlooper

    bjlooper Well-Known Member

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    This is a example of why I don't think we should imply that weight decreases wind Drift

    Nosler Partions .277 cal

    150 Gr. Ballistics B.C. 0.465 S.D. 0.279
    160 Gr. Ballistics B.C. 0.434 S.D. 0.298

    assume the same MV the 150 gr will drift less and shoot flatter than the 160 gr Partition

    DR B
     
  13. abinok

    abinok Writers Guild

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    am I missing who said weight decreases wind drift? Everybody so far has qualified that by adding high BC
     
  14. bjlooper

    bjlooper Well-Known Member

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    I guess the point I'm trying to make is that I see to many people assuming that weight and caliber are the deciding factors, and they are not.

    We have all seen the post that say I use a .223 win for varmits except on windy day then I use my .243.
    A fast twist .223 shooting 80-90grVLD bullets will smoke a 243 factory twist shooting 85 gr corelocks.

    Dr B