Bullet BC and wind drift, wrapup.

[model14]

Boyd

If a bullet is only pushed to the side and the nose does not turn to follow the wind then it would resume it's original direction once it is past the wind. If you are shooting 1000 yards and there is a 1 MOA crosswind from the muzzle out to 100 yards, and then calm from 200 yards to the target, are you saying that the wind deflection at the target will only be 1"? I wish it were so. That's why the wind closest to the muzzle is the most important. Once the bullet turns to follow the wind that's the direction it will continue on until changed by other factors.

Ray

Ray,

Please describe "follow the wind". Are you saying a bullet turns left when encountering a cross wind from the right? If so that is totally counter to what I have always thought and observed (airplanes, sailboats, arrows, etc.). Do you know what "heave to" means in regard to a sail boat? It means to center the mainsail boom and let the boat run free into the wind. It turns into the wind, always. So does my airplane when the wheels leave the ground and so does the arrow I shoot.

I guess it is possible that if the center of gravity is aft of the center of pressure of the bullet, and there was no spin stability, then a downwind turn could happen. I just don't see it. maybe I have always been wrong and didn't really see what I thought I was seeing and feeling.

Anyway, it is just a discussion which isn't going to make either one of us shoot better.

Richard

 

[Boyd Allen]

Model 14,
I think that the key ,in your examples, is where the center of pressure is relative to the center of mass. For spin stabilized elongated bullets, the center if pressure leads. for an arrow, or weather vane, it trails the center of mass, in the first instance, and the point of rotation in the second.

 

[Cheechako]

Ray,
. . . I should also add that this is what I think. Knowing has a higher standard of proof.

Boyd

Ballistics is physics. It doesn't matter what one thinks or what they think they know, nor does it require proof. It's the law. You can't change any of it no matter how little sense it makes to us.

Richard

By "follow the wind" I mean the nose of the bullet will turn in the direction of the wind. A 3 oclock wind, the nose will turn to the left, etc. Boyd's statement that it's the center of pressure vs the center of mass is close to a better description. The same principal applies to a bullet's ability to follow it's trajectory rather than always maintaining a nose up attitude as when it leaves the muzzle. If that didn't happen, an artillery projectile would not hit a target fuze first.

I don't think most of your examples are valid because boats and airplanes have rudders, rockets have fins, etc.

If you are flying and encounter a side wind you turn into the wind to maintain the relative heading. But if the wind stops you will continue on a different heading until you make a rudder adjustment. Unfortunately, with a bullet we cannot make mid-trajectory adjustments.

Ray

 

[Boyd Allen]

Ray,

Unfortunately, the laws may be misapplied. What needs proof is whether the laws have been correctly applied. Saying that "it's physics" does not get anyone a pass on that.

Boyd

 

[Cheechako]

Boyd

I tend to think the big kids know how to apply the laws. Otherwise we couldn't land on Mars, or shoot down one bullet with another bullet, etc. It's us commoners that tend to disagree with the laws as in, "I know that can't be true 'cause I have seen instances of that bullet doing just the opposite." "You can't tell me a 6mm bullet has less wind deflection than my big Magnum." "What may work on paper doesn't apply to the real world."

Ray"

 

[alinwa]

Boyd

I tend to think the big kids know how to apply the laws. Otherwise we couldn't land on Mars, or shoot down one bullet with another bullet, etc. It's us commoners that tend to disagree with the laws as in, "I know that can't be true 'cause I have seen instances of that bullet doing just the opposite." "You can't tell me a 6mm bullet has less wind deflection than my big Magnum." "What may work on paper doesn't apply to the real world."

Ray"

It wasn't 5yrs ago that everyone insisted that "anything learned in a tunnel is useless because you'll never be able to tune for the real world!"

What a crock

al

 

[Big Gunner]

Richard,

I'll answer your questions. Please don't get discouraged.

If a spin stabilized bullet encounters a cross wind, the difference in drag force on the upwind and downwind side of the bullet, will result in the bullet turning into the apparent wind to the point where the drag forces become equal.

Essentially, Yes.

The effect the wind has on bullet drift is strictly a function of BC (sectional density and form/shape factor) and lag (the time of flight difference caused by bullet slowdown).

Yes and no. Yes the effect the wind has on bullet drift is strictly a function of BC. No it is not caused by the lag time, but by the bullet slowing down in a direction different than the original glide path do to the bullet tuning into the wind.

A "side profile" BC need not be considered because the apparent wind is acting along the longitudinal axis of the bullet.

Correct.

The weight of the bullet is already taken into account by the BC and the muzzle velocity is part of measuring lag time.

Correct.

Therefore, the highest BC bullet will always have the least drift in a cross wind.

Correct. All other variable being equal.

The highest BC bullet may not be the most accurate bullet to shoot.

Correct.

There, I think I have it in a nutshell.

Absolutely!

Thanks all for your patience.

Thank you for initiating the thread.

Lisa Spendlove

 

[alinwa]

wow

nicely done Lisa!

al

 

[Old Gunner]

It wasn't 5yrs ago that everyone insisted that "anything learned in a tunnel is useless because you'll never be able to tune for the real world!"

What a crock

al

When I was much younger it was called "the Jesus factor", when everything works out perfectly on paper but it still blows up on the launch pad or misses Mars by three million miles. Then the engineers say "Jesus H Christ on a pony what happened?".