Attention all ballisticians

WOW!:eek: What can I say. Richard is right and McDonald & Almgren are wrong.

In the words of Ned Pepper, "I call that bold talk for a one-eyed fat man." If you'll recall, that got poor old Ned shot. ;);)

Ray

Ray,

Call me a one-eyed fat man, and I no I won't shoot you :D, but
McDonald & Almgren are wrong, period. That's my story and I am sticking to it.

I don't have a problem finding fault with something someone wrote in a book. I hope you don't either. There is a lot of bad information out there. We are probably reading their statement that you quoted out of context. If we read everything they say on the subject, it may well be interpreted differently.

Keep challenging me, keeps me on my toes at 68 years young.

Richard
 
Then I have a simple question

If it is not increased drag that causes the bullet to get to the target slower, what physical force is it?

I'm at a loss to explain what force (other than drag) effects the velocity.

Thanks,

Lisa
 
Richard,
Drive your car at 50 mph in calm air, stick your hand out the window and feel the drag force. Put the car in neutral and note how quickly it decelerates. Now drive at the same speed into a 50 mph headwind and do the same tests. You should find that the force on your hand is much larger, because drag depends on your velocity relative to the air (100 mph), not to the ground (50 mph). The car will slow down faster, again because the drag is greater. The same thing happens to the bullet.

Cheers,
Keith

Keith,
You are mixing apples and oranges. The force on your hand with a 50 mph headwind is much greater because you are attached to the ground through the wheels of your car. If you cut your hand off the effect of the headwind will quickly disappear. Not immediately though, because of the hand's inertia. And.. the subject of inertia is what is causing much of the confusion here in this thread. I will address that in my answer to Lisa.
Richard
 
Have you actually measured drag?

I do know that a 20 fps headwind does not increase drag on the bullet all the way to the target; perhaps in the first few inches or maybe even feet but not beyond that.

I also know that a 20 fps tailwind does not decrease drag and that what I'm seeing on the target in the real world does not jive with what I'm hearing here.

Gene Beggs

Gene,
Respectfully, how do you know that drag is not increased or decreased? Directly measuring drag on a bullet requires a supersonic wind tunnel, or other advanced instrumentation. Drag can be calculated from the rate of bullet velocity loss found from chronograph measurements at multiple ranges. Have you done this, or are you inferring what happens to drag from what you see on the target? Could it be that an effect other than drag is causing what you see? Maybe a change in lift? (You do have a knack for posing interesting questions.:))

Cheers,
Keith
 
Let's make it a plane then

Keith,
You are mixing apples and oranges. The force on your hand with a 50 mph headwind is much greater because you are attached to the ground through the wheels of your car. If you cut your hand off the effect of the headwind will quickly disappear. Not immediately though, because of the hand's inertia. And.. the subject of inertia is what is causing much of the confusion here in this thread. I will address that in my answer to Lisa.
Richard

Richard,
The wheels don't matter in determining the speed of your hand relative to the air. If you prefer, change the car to a plane with 50 mph groundspeed in a 50 mph headwind. Hold a windspeed meter out the window and it will read 100 mph. The meter (and a bullet) experiences the sum of groundspeed and windspeed, and accordingly has higher drag.

Cheers,
Keith
 
Okay, a lightbulb flashed over my head

A very dim lightbulb, but.

I can see where some of the confusion is coming from. When Richard mentioned inertia, I saw where I am having trouble communicating my thoughts.

Going out on a limb here by not waiting for Richard's response to my question:

I was not clear in stating that (in my opinion) the bullet experiences increased drag to to the increased airspeed, BUT NOT FOR THE ENTIRE TRIP DOWN THE GLIDE PATH.

I believe Richard is going to tell me that increase in airspeed (and therefore increased drag) only happens for a very finite and very, very, very short period of time.

Once the inertia of the bullet (which is the same whether or not there is a head or tail wind) overrcomes the force exerted by the increased drag, the bullet reacts the same as it would if there were no head or tail wind.

I agree completely with the above statement. I knew it going in, but was unable to communicate it clearly.

Once the momentum of the bullet in a headwind reaches the momentum it would have had if there were no headwind, drag is EXACTLY the same.

An airplane analogy would be: For a brief period of time when an airplane lifts off the ground in a headwind (at that moment when the wheels first leave the ground), there is increased drag. Once the airplane is stable in flight, the plane never feels the headwind again.

The same would be true with the bullet. It would only take a few miliseconds to overcome increased drag, but that increase in drag is there nonetheless and this is what affects flighttime.

I am sorry if I inferred that I thought there was increased drag all the way to the target. That was never my intention.

Any, hey. If I'm wrong, I can eat crow with the best of them. As I said earlier, I am a STUDENT of the rifle. I am always will to learn something else.

Lisa
 
2. Any degree of headwind results in my bullets striking high; a tailwind causes them to strike low.

Gene Beggs
Angle of Repose, and launch angle
There is ever so small an amount of lift imposed - a head wind will increase that lift, and tailwind decreases it. Of course this is really only true until the bullet reaches just beyond the apex of it's trajectory.

And I would guess that there is a very small component of increased drag all the way to the target - and here's why I say that. In a 20fps head wind - there is still 20fps worth of drag being placed on the bullet while it is standing completely still - any motion at all adds the component due to motion on top of that. But then again 20fps worth of drag is hardly noticeable in the data "noise" of all other factors. Much less than 1% for most shooters besides rimfire where it's still smaller than the normal range of MV variation.
 
OK. I'm still confused. Maybe even more than I was before.

You say that a bullet experiences drag from muzzle to target. With a headwind, that drag is increased, but only for a very brief period after which the drag returns to it's original force.

That doesn't make sense to me. It sounds like we're trying to re-write Mother Nature's laws.

Can someone explain that to me? In simple words, please.

And while I have your attention, no one has answered another question that I asked earlier. I said that a bullet will turn to follow a crosswind (deflection) but some said, no that's not true. So I asked, OK, what does cause the deflection? No response as yet.

Ray
 
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A very dim lightbulb, but.

I can see where some of the confusion is coming from. When Richard mentioned inertia, I saw where I am having trouble communicating my thoughts.

Going out on a limb here by not waiting for Richard's response to my question:

I was not clear in stating that (in my opinion) the bullet experiences increased drag to to the increased airspeed, BUT NOT FOR THE ENTIRE TRIP DOWN THE GLIDE PATH.

I believe Richard is going to tell me that increase in airspeed (and therefore increased drag) only happens for a very finite and very, very, very short period of time.

Once the inertia of the bullet (which is the same whether or not there is a head or tail wind) overrcomes the force exerted by the increased drag, the bullet reacts the same as it would if there were no head or tail wind.

I agree completely with the above statement. I knew it going in, but was unable to communicate it clearly.

Once the momentum of the bullet in a headwind reaches the momentum it would have had if there were no headwind, drag is EXACTLY the same.

An airplane analogy would be: For a brief period of time when an airplane lifts off the ground in a headwind (at that moment when the wheels first leave the ground), there is increased drag. Once the airplane is stable in flight, the plane never feels the headwind again.

The same would be true with the bullet. It would only take a few miliseconds to overcome increased drag, but that increase in drag is there nonetheless and this is what affects flighttime.

I am sorry if I inferred that I thought there was increased drag all the way to the target. That was never my intention.

Any, hey. If I'm wrong, I can eat crow with the best of them. As I said earlier, I am a STUDENT of the rifle. I am always will to learn something else.

Lisa


And Lisa, here it is (written before I read your post):

What is causing the confusion in my statements and in interpreting others, is that I have not been taking into account the inertia of the bullet.

Inertia is the property of an object which opposes a change in velocity. It is proportional to the objects weight.

When a force, such as drag, acts on an object, how fast it decelerates (slows down) in a headwind, or speeds up (accelerates) in a tail wind, is very dependent on the objects inertia.

Wind shear is a rapid change in the winds velocity. How much force the wind shear exerts on an object is a function of the objects weight, and how much and how fast the wind velocity changed. A light object is not affected by wind shear as much as a heavy object, because a light object has less inertia than the heavy object.

As a bullet leaves the muzzle and proceeds down range it may encounter all sorts of different wind shears (headwind, tailwind, cross wind, updraft downdraft, boil, etc.). These different winds can be steady or gusty.

Assuming there is no wind, the bullet is strictly creating its’ own wind. This wind, or flow of air, is in a direction opposite to the bullets flight and creates a drag proportional to the square of the bullets speed. The bullet slows down due to the force of the drag (F=MA) and takes a certain amount of time to reach the target. During this time, gravity acts to cause bullet drop.

To answer Lisa’s question, a bullet leaving the muzzle into a 100 mph headwind, will immediately experience a large wind shear (an abrupt increase of 100 mph in the wind speed acting on the bullets surface). Because of the bullet’s inertia it cannot immediately slow down. Therefore there is an increase in drag relative to what it would be without the 100 mph headwind. In this case headwind causes an increase in drag.

However, this increase in drag only lasts long enough for the bullet to lose 100 mph in velocity relative to what the speed would have been if there was no headwind. As soon as that happens, the headwind is no longer causing an increase in drag force over and above what it would have been without the headwind.

A light bullet (30 grain 22LR) will lose that 100mph very rapidly as compared to a 300 grain (.338 Lapua Magnum) heavy bullet. This is due to a ten fold difference in the inertia of the two different bullets. The heavy bullet is “bucking” the wind better than the light bullet.

I have no idea, nor does probably anyone else, how quickly the 22 will lose the 100 mph. Maybe it is within the first 10 feet, or maybe it takes all the way to the target. In any event the 300 grain bullet will take a whole lot longer.

The same event will occur if the bullet leaves the muzzle with no headwind or tailwind but encounters a change in wind on its’ way to the target.

Drag does not cause a bullet to drop, gravity does. Drag causes a bullet to take longer to reach the target so gravity has a longer time to act on the bullet.

The statement that drag increases in a headwind, or decreases in a tailwind, is only correct for a wind shear situation (an abrupt change in wind velocity). How much the drag will change due to the wind shear is proportional to how much the wind changed, how fast it changed, and how much the bullet weighs. Very complex, to say the least, as is the flight of the bullet.

From a purely academic standpoint, a very light body, encountering a very small change in wind speed, can change its’ ground speed fast enough to not feel a noticeable increase in drag.

I stand corrected in being wrong to view this question as a bullet already immersed in a headwind (academic environment) without having considered how it got there (real world). In the first case there is no increase in drag, in the real world there is due to wind shear and the bullets inertia.

Ray, I still don’t like the flat out statement made in the book you quoted. A clarification by the authors would have been in order. They should at least address the large difference in drag increase due to the variables of wind velocity amount and rate of change, and bullet weight

Lisa, I hope I answered your question.

Here is the real world:

At the 600 yard range yesterday, the wind was all over the place, doing every dance imaginable. My .260, with a 142 grain bullet, smoked everyone else because they were trying to chase the wind changes with their 22’s and 6mm’s and I was just holding dead on the X and shot a F Class 194-4X (20 shot string). Inertia wins every time.

Richard
 
Thank you lisa!

A very dim lightbulb, but.

I can see where some of the confusion is coming from. When Richard mentioned inertia, I saw where I am having trouble communicating my thoughts.

Going out on a limb here by not waiting for Richard's response to my question:

I was not clear in stating that (in my opinion) the bullet experiences increased drag to to the increased airspeed, BUT NOT FOR THE ENTIRE TRIP DOWN THE GLIDE PATH.

I believe Richard is going to tell me that increase in airspeed (and therefore increased drag) only happens for a very finite and very, very, very short period of time.

Once the inertia of the bullet (which is the same whether or not there is a head or tail wind) overrcomes the force exerted by the increased drag, the bullet reacts the same as it would if there were no head or tail wind.

I agree completely with the above statement. I knew it going in, but was unable to communicate it clearly.

Once the momentum of the bullet in a headwind reaches the momentum it would have had if there were no headwind, drag is EXACTLY the same.

An airplane analogy would be: For a brief period of time when an airplane lifts off the ground in a headwind (at that moment when the wheels first leave the ground), there is increased drag. Once the airplane is stable in flight, the plane never feels the headwind again.

The same would be true with the bullet. It would only take a few miliseconds to overcome increased drag, but that increase in drag is there nonetheless and this is what affects flighttime.

I am sorry if I inferred that I thought there was increased drag all the way to the target. That was never my intention.

Any, hey. If I'm wrong, I can eat crow with the best of them. As I said earlier, I am a STUDENT of the rifle. I am always will to learn something else.

Lisa



Lisa, you explained it beautifully! :D

That's it; I think that is exactly what happens. :)

Gene Beggs
 
Yep, I think you're right.

Angle of Repose, and launch angle. There is ever so small an amount of lift imposed - a head wind will increase that lift, and tailwind decreases it. Of course this is really only true until the bullet reaches just beyond the apex of it's trajectory. QUOTE]



Vibe, I think you have hit the nail on the head!

This perfectly describes what I have had in my head for years. Thank you. :D

Gene Beggs
 
And I would guess that there is a very small component of increased drag all the way to the target

Yes, at least out to a certain range. Drag depends on airspeed. In your example, even at 500 yards, the bullet with headwind still had a 5.5 fps higher airspeed than the bullet with no wind.

Cheers,
Keith
 
Getting back to bullets, a headwind will cause a change in a bullets trajectory that is roughly equivalent to lowering the bullet's BC, This effect is maintained as long as the bullet is in flight and the wind is the same. The reverse is true for a tail wind. On a day with a good stiff breeze, first throw a ping pong ball into the wind, and then with the wind.
 
I'm willing to try it one more time

Okay,

A bullet leaves the barrel at 3000fps. This is the ground speed.

This bullet has a drag force of "X". This is primarily derived from it's size, shape, and initial velocity.

The bullet will constantly decellerate all the way to the target due to drag.

The bullet does not ALWAYS have a drag force of "X", however. "X" is only the drag force at the initial 3000 fps velocity.

At any other place in the bullets flight time, the drag force will either be "X" plus something, or "X" minus something.

When the bullet slows to a speed of 2999 fps, the drag is less than it was at 3000 fps. Therefore, the drag force is "X" minus 1 fps of drag.

When the bullet slows to a speed of 2998 fps, the drag is now "X" minus 2 fps of drag.

This happens all the way to the target. Less velocity, less drag, constantly.

Now let's throw in a headwind.

The bullet leaves the muzzle at 3000 fps and encounters a 14fps headwind (about 10 miles per hour).

The drag force is equivelant to "X" plus the added drag equal to 14fps. Another way to say this is that the bullet encounters a drag force equal to a forward velocity of 3014 fps with no headwind. This is the airspeed.

This added drag slows the bullet down faster than if there were no headwind.

Then the bullet slows to a speed of 2999 fps (in the same 14fps headwind) and the drag force dimishes by a force equal to 1fps or to the drag experienced by an airspeed of 3013 fps.

This added drag happens along the glide path until the bullet fired into the headwind slows to an airspeed equal to that of the initial muzzle velocity (3000 fps), at which point the bullet exhibits the exact same amount of drag as it would have if it were fired without the darn headwind.

The difference in point of impact is caused by gravity having a longer period of time to act on the bullet because the time of flight was longer due to the increase in drag as a result of the headwind imparting an increase in the velocity of the air surrounding the bullet during a portion of its flight.

I think that this last paragraph is what I said in first place.

I hope I did a better job this time, because if this isn't clear, I can't do it any better without drawing pictures and weaving/waving my hands around.

Lisa
 
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Ray,

I'll give you my take on the question of a bullet turning "into the wind" or "pointing into the wind".

Most of this is copied from my post on the other wind drift thread but I did change a couple of things to make it easier to read. I did not change the content.

Caution—At this point I am oversimplifying—Caution

Mostly, what I believe on the issue of bullet flight is this: Everyone gets caught up in the “what would happen in a vacuum” vs. “what happens in the atmosphere” debate.

I think most of the discussion would become easier to understand if we debated “WHAT WOULD HAPPEN IN THE ABSENCE OF GRAVITY”.

With the absence of gravity, but not in a vacuum, all of the forces that affect the bullet are present; the bullet just never falls to the ground.

What happens if a bullet is fired in the absence of gravity?

If it is fired on a level plane, it will continue to travel dead ahead (wind, the coriolis, magnus, and other forces excluded for the moment) until its forward momentum stops.

If nothing else acts on the bullet except the drag created by coasting through the atmosphere, the bullet will continue to travel unimpeded and continue to bleed velocity until it comes to a dead stop, where is will just hang there as the earth rotates out from under it.

Likewise, it will ALWAYS bleed velocity directly opposite the drag (I know, it is really in the direction of drag, but it is easier to think of it as opposite). THIS IS THE PART THAT CAUSES WHAT MOST PEOPLE REFER TO AS "WIND DRIFT".

If we impart a 90 degree crosswind on this bullet (in the absence of gravity) as it is flying along, it will precess (pointing its nose into the crosswind) and, as it bleeds velocity directly opposite its drag, it will slow down in the opposite direction of its nose. Again, this is what most people refer to a “wind drift”.

As the bullets’ velocity approaches the velocity of the crosswind the bullet will precess further and further into the wind. When the forward velocity is the same as the crosswind, the bullet will precess at a 45 degree angle to both the wind and original direction of travel. When the forward velocity decreases to zero, and if the crosswind is still blowing, the bullet will precess directly into the crosswind (or be completely sideways to the bore). Eventually, the wind would start pushing the bullet backwards. In other words, pushing the bullet ass backwards accelerating the bullet until it reached a speed equal to the wind velocity.

This is why, if a bullet is fired from one balloon moving in an air mass, at a target fixed to another balloon traveling in the same air mass, the bullet will still exhibit “wind drift”. It is this precession, and the corresponding velocity loss in the opposite direction of drag that causes the bullet to “drift”.

This is why a fired bullet and a bullet dropped from sufficient height to achieve terminal velocity do not exhibit the same amount of “wind drift”.

"Wind Drift" is caused by the bullet slowing down in a different direction than the direction is was fired in.

Anyway, that’s what I think.

Lisa
 
Boyd,

Your analogy with the ping pong ball is good. Finally I approve of your introduction of round ball imagery (I know you're relieved) although I must point out that unless launched with a wicked slash of the paddle, there probably isn't much spin in this ball example.

Greg
 
Vibe and Gene,

A headwind doesn't lift a bullet by blowing on the bottom of it until it reaches apogee anymore than a crosswind blows on the side of a bullet. In both cases the bullet aligns itself to the air it sees. Launched on an upward trajectory, a bullet traveling into a horizontal headwind will point slightly lower compared to the horizon than into still air. And it slows down along its own axis after it aligns itself. So in a headwind a bullet will strike the target lower.

Except, just as Gene has observed, I also get low hits with a blow from behind and high hits from a headwind. With a Palma rifle at 1K substantial push from dead ahead will produce a high nine ring hit and a similar tailwind will produce a low nine. This is backwards from what the models predict, so what is going on?

In long range benchrest I can't see the results for record while shooting. I have to wait for the target to come back. So I take my time as fast as I can and try to get my shots off in a single condition. Sometimes that works.

In long range score games (F-Class, Palma etc.)you have to wait for each shot to be scored before you can proceed and conditions don't prevail for many shots, especially where you have motorized (slow) pit service as at Butner. And these elevation changes that are contrary to the model really show up.

I think this is due to the topography of the ranges I shoot. Butner, Oak Ridge, Hawks Ridge and Williamsport all have dramatically elevated firing lines that induce a vertical up component in a headwind and the opposite in a tail wind. Other ranges I shoot at (Quantico, Ohio, Pella, Piedmont and Pierre have elevated firing lines but not so pronounced and of less dramatic effect. This effect of course occurs where drag is greatest and diversion from line of sight is greatest over the flight of the bullet as Al so well illustrated in his sketch of some time ago.

That's my story and I'm stickin' to it.

Greg
 
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Boyd,

Your analogy with the ping pong ball is good. Finally I approve of your introduction of round ball imagery (I know you're relieved) although I must point out that unless launched with a wicked slash of the paddle, there probably isn't much spin in this ball example.

Greg

So steenking FIRE ye pingypongy ball through a rifled barrel...... :)

I applaud Boyd for sticking to the root of the thang.

root ON Boyd!

al
 
Lisa,

I'm with you until your statement about wind drift of a bullet fired between two floating balloons. If they are floating in the same air, how can there be wind or bullet drift between them? Do you mean in relation to the ground or each other?

Greg
 
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