Wind Calculations Brain Teaser

Discussion in 'Long Range Hunting & Shooting' started by Bull45cal., Mar 20, 2008.

  1. Bull45cal.

    Bull45cal. Well-Known Member

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    Alright guys, I need some help! I am trying to come up the a scaled down version of my hunting cartridge for practice. I'm in NC, so I don't have lots of long ranges with which to practice. I was feeding numbers into my ballistics calculator, and it is not telling me what I want to hear. If the flight time of two rounds is the same, and the BC is as well, would not the wind movement be also? What am I missing?

    Thanks,
    Shane
     
  2. edge

    edge Well-Known Member

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    IMO, no, but I have been wrong before :)

    A .22 and a .511 bullet with the same BC certainly have a far different profile in the wind, and I would think that the 50 cal would be pushed further.

    edge.
     

  3. ss7mm

    ss7mm Writers Guild

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    I used Exbal with 2 different bullets. One at 100 grains and one at 400 grains and both with a BC of .300 and both launched at the same muzzle velocity. All weather factors are set at the same values.

    If you use ballistic software you will find that if you have a 100 grain bullet with a BC of.300 and a 400 grain bullet with a BC of .300, for the time of flight to be the same the muzzle velocity would have to be the same and this isn't likely to happen although it's theoretically possible.;)

    All ballistic factors would be the same at all yardage intervals with the exception of energy. The advantage goes to the heavier bullet in the energy department.:)

    The answer to your question is a theoretical Yes.;)

    [​IMG]
     
  4. Bull45cal.

    Bull45cal. Well-Known Member

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    Thanks guys, just want to clarify something, and get you to weight in again. I'm using 155gr. A-Max. for long range. I want to develop a short range load that will just be a scaled down version (same bullet) of the long range version. One load is around 3000fps, and the other is around 1400fps. The flight time is the same, the weight is the same, the B.C. is the same (Well closely since B.C. of a bullet is dependent on velocity), shouldn't the effect of the wind on the two bullets be the same?

    Bullet 1 with flight time A being pushed by wind B should = X

    Where Bullet 1 = Bullet 2 then,

    Bullet 2 with flight time A being pushed by wind B should = X


    Is this not right?

    Thanks,
    Shane
     
  5. ss7mm

    ss7mm Writers Guild

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    If one has a velocity of 3000 fps and the other has a velocity of 1400 fps then how can they possibly travel from point A to point B in the exact same amount of time???:confused:

    With that much velocity difference the time of flight is going to be quite large.;)

    If you're talking about the time of flight dictating the distance traveled at the different speeds then the effect of the wind would probably be the same, it's just that the distance traveled by each, at different speeds, is going to be far different.

    See below. I didn't look up the BC, I just put a value in. The end result still displays what happens.

    [​IMG]
     
    Last edited: Mar 20, 2008
  6. edge

    edge Well-Known Member

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    I think that a bullets BC is based on velocity. This may be very important if you are going to launch it at 1400 fps since you run the risk of going transonic.

    edge.
     
  7. Bull45cal.

    Bull45cal. Well-Known Member

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    Yes, to both of you. Thanks for your input. I am shooting the 1400fps round a close range (100-200yrds). The 3000fps is for Intermediate Range (300-600yrds). The flight time is will be very close, and so will bullet path. I just could get my ballistics software to agree with me about wind. Below is what I should have posted first, but I was frustrated and not thinking straight. Thank you both for your assistance. I'm much calmer now, and can think more clearly. I don't have enough patients for inanimate objects (computers).

    Thanks Guys,
    Shane

    Notes:
    IR Load; 155gr. Hornady A-Max with 0.435 BC, MV @ 3000fps, Zeroed at 200.

    Practice Load; 155gr. Hornady A-Max with 0.435 BC, MV @ 1400fps, Zeroed at 77 (I think).
     
  8. milanuk

    milanuk Well-Known Member

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    If you don't need to fire from the same gun... it's been said that a .22LR @ 200yds drifts in the wind about the same as a .308 / 155gr Palma load (which you are very nearly at) @ 1k, given the size of the targets and all. So you might take a look at your rimfire and spend some time shooting at 100-150yds with it, and really save some $$$.

    Just a thought,

    Monte
     
  9. ss7mm

    ss7mm Writers Guild

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    If you're talking same gun, same cartridge, same bullet just a greatly reduced powder charge to get the lower velocity I'd suggest that you be careful of shooting greatly reduced loads. I've never tried them and probably never will but there are some bad stories about results of shooting greatly reduced charges as compared to full loads.

    Give it some thought and maybe post the gun, cartridge etc. and see if anyone on here has shot reduced loads of that level in their similar gun.;)
     
  10. Bull45cal.

    Bull45cal. Well-Known Member

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    Thanks Milanuk,

    I practice with my .22 alot. I guess I just need to use it for more than just trigger practice.

    Thank you ss7mm as well. Here is what I'm using currently 13.5gr Red Dot in .30-06 Springfield (Remington Cases), CCI 200 primers, topped with 155gr Hornday A-Max. Shoots well in my Savage 110E.

    Thank all you for your help.

    Shane
     
  11. cdoubleu

    cdoubleu Member

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    Here is how it works: Gyroscopic Stabilization and Aerodynamic forces. You fire one round with at 3000fps and one at 1400fps, from let's say arbitrarily from a 1:12" Twist rate barrel. The bullets are rotating at different speeds (3000 rotations per second and 1400 rotations per second) and producing different induced forces (thing back to physics- that right hand rule, aerodynamics-wind cocking, spin induced yaw, etc). Time of flight may be the same for your scaled ranges but the forces are not. To get back to the induced forces... if I drop a bullet in the wind from a fourth story window it will impact on level ground the same time as if I fired a one level, but the wind drift will not be the same, it will be substantially less than the fired bullet (doesn't that stink). In those two or so seconds, the bullet is not being pushed by wind alone. Resisting forces increase (and not proportionally, but exponentially) with velocity. That is why your wind drift is different. Fluid dynamics are not directly scalable with size or velocity, so you've got a losing experiment for your purposes by retarding your load. Just like sex, nothing is like the real thing.
    If you are interested in getting a reduced load for whatever purpose, go to a high volume powder like Trail Boss. With a lot of extra space left a case you risk detention vice the desire deflagration. Detenation is very bad and may cause catestrophic destruction of your rifle.
     
  12. MontanaRifleman

    MontanaRifleman Well-Known Member

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    Only if they have a different velocity. There are only two things that affect wind resistance... BC and velocity... that's it... nothing else... Having said that, a 50 cal bullet will almost certainly have a greater BC than a .22 cal.

    If a 22 cal bullet has the same BC and velocity as a 50 cal bullet. both will have identical trajectories, TOF's, down range velocities and wind deflections. Get your ballistics calc out and check it out.