Well I thought I understood all this but I am probably mistaken. Did we ever resolve the "mystery" of the difference in wind drift between dropping a bullet and firing a bullet? Would a bullet dropped actualy drift 1", or are we just going to explain it all away by saying it is all due to bullet spin and yaw? If it was, wouldn't this be a factor even if no wind was present? Just curious, but don't want to start an acrimonious discussion.
Peter.

.

Thanks Alf. Let me rephrase if I can. I think you are saying that if I lasered the barrel and then shot a round, with no wind, the bullet would not strike in a vertical line with the laser dot. It would be off to one side or the other depending on twist direction. The addition of wind would add to or detract from this "deviation" for want of a better word. We do not notice this because we just adjust the sights to compensate for the "windless" condition. Is that something like what you are saying?
Peter.

.

Oops! I thought this was the wind drift thread

Alf,
I see now why you are so belligerent about the silly idea that weight is factor in wind drift. You are confusing wind drift with other external ballistics such as overturning moments, yaw of repose, Magnus force and a host of other issues that are quite separate from wind drift. While all play their part from muzzle to target, wind drift and weight remain unconnected.

Kudude, some more silly numbers for you about wind effects. One of the tombs I read awhile back had an example of the effects of Aerodynamic Jump, a fairly extreme case as it relates to sport shooting. It seems that the difference of POI between two B17 waist gunners(M2, one firing to the right, the other to the left) firing at a target 600 yards off to the side of the bomber would be about 16' IIRC. This is on the vertical plane mind you, assumes the target is pacing the bomber which is motoring along at 250 mph. That is what AJ can do, but I haven't a clue how that will help anybody's shooting here on planet Earth.

I may not have quoted the figures precisely but you get the idea I hope.

Alf, in your discussion with Peter regarding "drift" in calm air, I presume you are speaking of what is often referred to as Spin Drift? If so, it too is a deflection caused by Yaw of Repose. One of the older British arms, perhaps the Lee Enfield, actually had an assymetrical elevation adjustment when the long range sight was tipped up that addressed this influence. Don't recall the actual amount but it was something like a foot or so at 1000 yards IIRC.

There is a thread on the small bore forum about the .204 kicking ass or some such. I'll link it with an edit in just a moment. Take a look at my comment about the relationship between weight/drag/diameter/BC etc. It might help with the bigger being better thing.

https://forums.accuratereloading.com/eve/forums/a/tpc/f/6711043/m/351102342

It is not the most lucid writing I've done and apparently I forgot how to spell spherical for some reason... Hope it makes sense.

quote:

Originally posted by Gerard:
I see now why you are so belligerent about the silly idea that weight is factor in wind drift.

Actually, if I had to rank the sillyness of this arguement I'd rank what you're saying to be just as, if not more silly than his.

It's pretty silly to claim that because an equation has more than one variable that one of the variables isn't a factor in the end result.

If X * Y = Z, it's really silly to claim that because changing Y changes the value of Z while holding X constant that X is "not a factor" or is "unconnected to" the value of Z.

Jon A,
If I claimed that painting flames on the front of my car made it faster, would you take the statement seriously? Fact is that painting flames on a car is as irrelevant to the speed of the car as bullet weight is to wind drift and such a claim would be ...... silly.

If weight would be a factor in wind drift, increasing weight will give a corresponding change in wind drift and decreasing it will give a corresponding and opposite change. This does not happen and Alf is arguing wind drift way out of context.

According to Robert Rinker, author of "Understanding Firearms Ballistics" there are several factors involved in wind deflection;time, weight,velocity. I will quote,"Weight is a factor as well because momentum is a result of weight times velocity and momentum tends to keep the bullet straight. If one bullet weighs 200gr and another 100, the heavier will be harder to push away from it's path." This makes sense to me. How about anyone else?

quote:

Originally posted by Gerard:
Jon A,
If I claimed that painting flames on the front of my car made it faster, would you take the statement seriously?

Poor analogy. Increasing the weight of the car without changing its aerodynamic drag would decrease its rate of deceleration due to aerodynamic drag while coasting from a given velocity. It would have a higher "BC." That's a better analogy.

Since this is so "elementary" to you, I'm starting to worry that you're purposely misleading/misinforming people. If you really do understand the physics behind it, you must be. But maybe you honestly don't.

quote:

If weight would be a factor in wind drift, increasing weight will give a corresponding change in wind drift and decreasing it will give a corresponding and opposite change. This does not happen

Yes it does happen if you leave all else constant. Changing X does change Z unless you also change Y at the same time.

Your example of different bullets of the same diameter, all weighing the same but having different BC's...you changed Y. You changed the Form Factor.

You could say the exact same thing for Form Factor that you are saying about weight: You can have numerous bullets of a given diameter all with the same form factor and only change the weight. The heavier ones will have higher BC's. They will drift less. So I guess Form Factor is meaningless?

In the end it's BC that matters. That is the end result, the answer to the equation one cares about for wind drift. Three physical variables go into it (excluding the minutia that will only serve to confuse people--form factor, square of diameter and weight). They all have an equal influence on the end result of BC. To say any one of them doesn't matter is simply incorrect.

quote:

Originally posted by D Hunter:
If one bullet weighs 200gr and another 100, the heavier will be harder to push away from it's path." This makes sense to me. How about anyone else?

That's exactly right.

Ballistic Coefficient is the end result that mattters. It doesn't describe a bullet's "sleekness." Or even the drag forces on the bullet. It describes how the bullet reacts to those drag forces--the end result.

"Sleekness," for lack of a better word is only a function of its Form Factor, or coefficient of drag. That alone tells you nothing. Not even the actual drag on the bullet.

To get actual drag, you also need its frontal area. This is proportional to the square of its diameter (which is 1/2 of the SD equation).

Now you can calculate the actual drag. That still doesn't tell you its BC--its rate of deceleration from a given velocity. So you still don't know the wind drift.

So, you add in weight (the other 1/2 of the SD equation). Now you can figure out the rate of deceleration that these drag forces will cause. The same force of drag (same form factor and diameter) on a bullet twice as heavy will decelerate it only 1/2 as fast per Sir Isaac.

So, it has twice the BC.

Jon A,
Give me a comparison of wind drift of two typical commercial cartridge loads.

A Federal 100gr 243 at around 2950 fps with the Nosler Partition.

A Federal 225gr 338 Win Mag at 2800 fps with the Sierra Pro Hunter bullet.

quote:

"Sleekness," for lack of a better word is only a function of its Form Factor, or coefficient of drag. That alone tells you nothing. Not even the actual drag on the bullet.

Pardon my butting in again, but actual drag value is precisely what is represented by Cd or form. How the bullet REACTS to that drag involves other factors such as frontal area, form and momentum.

I think it important to maintain practical perspective on this issue because there are practical limits dictated by physics, and in the end it is BC(a measure of a bullets ability to overcome drag) that determines resistance to wind DEFLECTION. It is critically important that shooters understand that it is not DRIFT we are discussing. Bullets of twice or even three times the weight of another commonly have lessor BC than smaller caliber bullets, and will play second fiddle on the "Drift Tables". On occassion the big lumbering RN designs have better BC's than the little hot rod pills. Weight IS a factor in the calculation, but in and of itself is meaningless.

Robert Rinker wrote a pretty good book for the person just warming up to the world of ballistics but his prose, written to the lay person, is not always precisely correct as a result. You may think that TOF is the mantra for calculating bullet deflection and you would be wrong. It is part of the equation, like weight is to BC, but its presence in the formula relates to drag, nothing more. Rinker alludes to this in his discussion regarding the difference in deflection between the .22 RF Hi-vel vs. Match ammo, the latter having longer TOF but less drift. Same form, same weight, different drag value because of velocity. Different BC. It is not something unique to the .22 RF, but affects all bullets regardless of caliber, weight, form, phase of moon...

Practical limits are determined by physical limits of materials as well as physics. How much pressure can the gun take, how fast can you spin a bullet before it flys apart, how much does Yaw of Repose degrade BC, how little twist can you get away with and still stabilize the bullet? It is quite one thing to theoretically design a very small caliber bullet with extraordinary BC, it is a different matter to put one on target. High weight for caliber infers faster twist rates, more bearing surface, higher chamber pressure for a given velocity, etc., ad nauseum. For a given bullet design aerodynamic overturning moments are greater at lower velocities which requires quicker twist rates. Cd is inverse to Mach number. The theoretical gain in BC as weight increases does not translate to practical reality in a proportional way, even if it is proportional to SD in the formula. All of this means that during part of a bullet's flight lighter/faster may well have a higher BC value for a given nose and base form. Shank length contributes little if any drag to the form, but it infers other issues.

Well, it is a complex environment and every time you rob Peter you gotta pay Paul. Don't loose sight of the Practical Big Picture while exploring fine points of theory. Focusing on a single issue may not give one the scenic view.

.

Alf and Jon A,

1. I have zeroed my 375 AI at 150yds on a windless day.
2. I have zeroed my 338 LM at 1000yds on a windless day.

What effect will wind of varying strengths (10, 20, 30mph) have on my shot placement at 150yds.
What information do you need to advise me on this?
What steps can I take to reduce the effect of wind on my shot placement? (Other than waiting for windless conditions.)

quote:

Alf says,
Now your analogy of the car holds no water cause you are making the classic mistake of drawing out a two dimensional vector graph and calculating the vector deflection of the car.

Alf,
You have this habit of giving explanations based on stuff that I did not say. I claimed the thing is faster after I spent half the night painting flames on it. You are blinding yourself with science and losing track of the original statement/question.

quote:

Jon A says
Poor analogy. Increasing the weight of the car without changing its aerodynamic drag would decrease its rate of deceleration due to aerodynamic drag while coasting from a given velocity. It would have a higher "BC." That's a better analogy.

What is it with you guys? I said it was faster. Top speed it higher and I shaved half a second off the quarter mile. It has to be the flames. Coasting down from a given speed is not an option.

Can't you guys recognise a silly statement if it walks up and bites you on the leg?

I wonder why Jon A is taking so long with the wind drift tables for the two Federal cartridges.

quote:

Originally posted by DigitalDan:
Pardon my butting in again, but actual drag value is precisely what is represented by Cd or form.

No, the Drag Force = 1/2 * density of air* Cd * Frontal Area * Velocity^2 . That's very basic fluid dynamics. If I tell you an object's CD, be it a bullet, car or airplane and its velocity you cannot tell me the force of drag because you don't know how big it is. A scale model built for wind tunnel testing with the same Cd will naturally have smaller forces of drag at the same velocity.

quote:

I think it important to maintain practical perspective on this issue

That's exactly what I'm trying to give people.

quote:

Weight IS a factor in the calculation, but in and of itself is meaningless.

Every part of the calculation has meaning or it wouldn't be part of the calculation.

quote:

You may think that TOF is the mantra for calculating bullet deflection and you would be wrong.

No, I've never said such a thing. In fact, I just corrected somebody here who was saying exactly that.

quote:

The theoretical gain in BC as weight increases does not translate to practical reality in a proportional way, even if it is proportional to SD in the formula.

Yes it does. Look at any two bullets of the same caliber with the same form factor but different weights and you'll see. Where this breaks down from a practical standpoint is it's very hard to change the weight of the bullet and keep the form factor exactly the same, even if you're trying to. Sometimes it gets better, sometimes it gets worse. But the proportional gain from SD is always there.

Gerard, which part of my prior posts did you not understand? Give me an example without also changing the caliber and form factor in an effort to confuse the issue.

quote:

Jon A,
Give me a comparison of wind drift of two typical commercial cartridge loads.

A Federal 100gr 243 at around 2950 fps with the Nosler Partition.

A Federal 225gr 338 Win Mag at 2800 fps with the Sierra Pro Hunter bullet.

I will try to make it simpler.

Give me a table stating how far each of the two bullets above will drift in 15mph crosswind at 100, 200, 300, 400 and 500 yards. If you cannot do both at the same time, first do one and post it. Then do the other and post it. To save you looking it up, the 243 has a BC of .408 G1 and the 338 is .430 G1.

This is a real life example. Something that 99% of shooters would find useful and would understand.

Yes, throw different weights as well as different calibers and forms resulting in different BC's and then give them different velocities and the average shooter will understand that perfectly. Let's try an confuse the hell out of them so they believe my point.

How about this instead. A 30 cal 175 SMK and a 240 SMK both launched at the same velocity. They're the same caliber, have almost identical form factors and they're lauched at the same velocity--3000 fps.

At 500 yds the 175 drifts 33.5" in a 20 MPH wind.
At 500 yds the 240 drifts 22.3" in a 20 MPH wind.

It drifts less because it has a higher BC. BC, the end result. But why does it have a higher BC?

It's the same caliber. Its form factor is nearly identical. If those are the only things that matter to a bullet's BC, tell me from where did the 240's increase in BC come?

BC, the end result, what matters. Once one understands what it means and where it comes from, then he can start throwing in other variables. Let's change the velocities to reflect what one could attain with each bullet from the same rifle. Any rifle that can push the 240 to 3000 should be able to push the 175 to about 3450. This lowers the drift of the 175 to 27.3".

Better, but the heavy bullet still kicks its ass.

Jon A,
Why is this so difficult? I am Mr. Average with two rifles and I would like to know what the wind drift of each is with the ammo I use. This is a question that gets asked regularly. Can you answer it or not? Both rifles are zeroed at 200.

I cannot believe that a klutz like me who flunked math in high school can come up with a question that a rocket scientist cannot answer.

I never said I couldn't answer it, only that the question has little bearing on your contention. If it makes you happy, the two will have very close to the same wind drift at 500 yds in a 15 MPH wind. 34.8" for the .338, vs 35.4" for the .243. (That's using BC's from the manufacturers--I'm not sure where you got the ones you list.)

The .338 has a slightly better BC but is being launched at a slightly lower velocity so many things are cancelling each other out to give similar end results. This in no way means that any one of those things doesn't matter.

Now answer my question, where does the higher BC of the 240 come from? And if it comes from something meaningless that is stuck in the calculation for no reason, why does it change the end results in reality?

Jon A...

quote:

quote:
"Sleekness," for lack of a better word is only a function of its Form Factor, or coefficient of drag. That alone tells you nothing. Not even the actual drag on the bullet.



Pardon my butting in again, but actual drag value is precisely what is represented by Cd or form. How the bullet REACTS to that drag involves other factors such as frontal area, form and momentum.

Cd is the coefficient formed by dividing the aerodynamic DRAG FORCE force by the dynamic pressure and bullet cross section area. In another take, BC is simply a non-dimensional value that expresses the ratio of weight to drag for a given projectile. Drag is proportional to Cd and Cross Sectional Area. That's basic ballistics.

Perhaps I could have chosen better words to express the previous thoughts. Attempting to explain this can be as educational to me as anybody else.

No, I can't do anything in particular with just BC or Cd without other info, it seems I alluded to that. Can you tell me the BC of a 160 grain bullet? Is is better than a bullet of 100 grains? That represents what I mean by being meaningless in and of itself. Once other factors are known we can do something with it.

The issue of proportionality in regards to BC and weight plays for a given caliber or a given weight as caliber changes if all else is equal, but you know that. Sure the BC formula says that BC is proportional to SD, my point is that in practicality it doesn't always work that way, as you said, things change. And that I think, is the nut of the whole discussion. Weight is part of it, not all of it, and it won't always hold sway in regards to wind deflection. Hornady makes a 225 gr. .338 cal bullet that has a BC of .397 IIRC,
and a .243 bullet of 105 grains with a BC of .500, so....

I don't think I directed my comment about TOF at you Jon. A lot of folks do not understand the point that it is part of the equation but has NOTHING to do with Wind Deflection. The value T-Tv does of course. It isn't the same thing. There is no residual magical influence of ToF in deflection, and every time I hear somebody say that less TOF means less drift I twitch a little.


Anyway, I've pretty much said all I have to say on this particular thread. I have my philosophy on the subject regarding this "weighty issue", perhaps others have their own. I've got other crats to skin besides this one. Y'all have a nice day!

Jon A,
Thank you for answering.

The higher BC of the 240 SMK comes from two things. More weight than the 175 and a much better shape. The ogive is fractionally longer as is the boat tail. It probably gains proportionally more BC from the better shape than from the weight.

Now to the dilemma you have with my 243 and 338. The 338 has more than double the weight of the 243 as well as a better BC. Why are the drift and trajectory results virtually identical?

Take a pair of 7mm 130gr Sierra bullets, a MatchKing with a BC of .395 and a Pro Hunter with a BC of .327 and shoot them at the same speeds. (Shooting light and heavy bullets of the same calibre at the same speeds as you suggest, to prove a theory is unrealistic.) The SMK will smoke the ProHunter on wind drift and trajectory. How can this be? The weights are the same. Where did the extra BC come from?

Now take that 130gr SMK and a 120gr monometallic copper bullet of similar BC value. Shoot the SMK at 2750fps and the copper mono at 3150fps. The mono will smoke the SMK on drift and trajectory. How can this be? It is 10gr lighter and has the same BC. Where did the extra resistance to drift come from?

(You may ignore the rhetorical questions above but I would like a response from you on the two below.)

Can we say the following is true?

Within the same calibre:

Trajectory and resistance to wind drift can be improved without changing the weight.
Trajectory and resistance to wind drift can be worsened without changing the weight.
Trajectory and resistance to wind drift can be improved even if weight is reduced.
Trajectory and resistance to wind drift can be reduced even if weight is increased.

Increasing or decreasing weight does not always bring a corresponding change in wind drift and trajectory.

Increasing or decreasing the BC always brings a corresponding change in wind drift and trajectory.

Increasing or decreasing the speed always brings a corresponding change in wind drift and trajectory.

So when someone asks what he can do to reduce the effect of wind and to flatten trajectory, do we tell him to look for bullets with a higher BC and shoot them faster or do we say to him to go find heavier bullets?

.

quote:

Originally posted by DigitalDan:
Cd is the coefficient formed by dividing the aerodynamic DRAG FORCE force by the dynamic pressure and bullet cross section area.

Exactly, as can be shown by re-aranging my above equation--when you know the equation for dynamic pressure.

quote:

Drag is proportional to Cd and Cross Sectional Area. That's basic ballistics.

Correct. And deceleration for a given force of drag is inversely proportional to weight. My point was BC accounts for all three equally, giving one a final answer while saving a bunch of math. But just because it does, doesn't mean the math that goes into it has less meaning. You'll get the same answer using a BC and a curve or doing it all the old fashioned way.

In order to do the latter, you need weight.

Although our terminology, etc, doesn't always match I think you and I are on the same page.

quote:

Originally posted by Gerard:
The higher BC of the 240 SMK comes from two things. More weight than the 175 and a much better shape. The ogive is fractionally longer as is the boat tail. It probably gains proportionally more BC from the better shape than from the weight.

Bzzz. No passing grade for you. Try doing the math again. The two bullets have nearly identical form factors (within 3% depending upon velocity) and yet the BC's differ by more than 40%.

quote:

So when someone asks what he can do to reduce the effect of wind and to flatten trajectory, do we tell him to look for bullets with a higher BC and shoot them faster or do we say to him to go find heavier bullets?

First, wind and trajectory should be looked at separately and a compromise struck depending upon the intended use (as one usually gets better as the other gets worse).

High BC is of course the final answer, and IF you can get a high enough one in a light enough package, choose the lighter package as it is more efficient (you can drive it faster). Nobody is refuting that final answer.

The bone I had to pick was with your claim that one of the three physical variables (frontal area, weight and form factor) which all have equal influence on BC had no effect on the final answer. That's simply wrong. No one of them means everything by itself obviously. That's why it's called an equation with more than one variable (remember high school algebra?). You can't get the final answer knowing any two of the three. You need all three. And all three have equal influence.

However, helping people understand what goes into that final answer and why can be helpful in many cases.

For example, some manufacturers advertise BC's that aren't realistic. Having a little common sense on the subject helps people call BS at the appropriate object when their real results don't match the computer programs (usually not the fault of the computer program).

Also, many smaller bullet makers don't give out BC's at all. Say somebody wants to use a particular semi-spitzer in his big magnum and wants one that drifts the least in the wind. They all look the same except for weight. Does he use the heavy one or the light one?

BTW, I don't work on rockets at Boeing. Just boring airplanes.

Gentlemen,

I honestly do not know why are you all making so much fuss about shooting in the wind.

Here is Walter's formula:

When shooting into the wind, aim low.
When shooting whith the wind behind you, aim high
When shooting with the wind from your right, aim right
When shooting with the wind from your left, aim left.

It worked guys, we finally lured Saeed out into the open veldt!

Saeed, while I agree with Walter's analysis, please ask him "How much left" or "How much right"?
Peter
PS. This thread seems to have been governed by considerably greater decorum than some others of recent vintage. I think I am learning something. Not quite sure what, just yet!

quote:

Originally posted by Peter:
Saeed, while I agree with Walter's analysis, please ask him "How much left" or "How much right"?
Peter
PS. This thread seems to have been governed by considerably greater decorum than some others of recent vintage. I think I am learning something. Not quite sure what, just yet!

Here is what Walter said:

"To determine how much you have to allow for the wind, stand and aim at your target - without any rest - and watch how far your aim is pushed off it. Then get down on a good rest, and aim the same distance the wind pushed on the OPPOSITE side"

Now you all know the secret of shooting in windy conditions - and why I am so tolerant!

Putting up with this sort of characters in our workshop, one has to develop extreme tolerance - or commit heinous crimes!

.

Alf,
I have some questions:

1. If the .308 above is zeroed at 200yds,
a) What would the spin drift distance be at 500yds and
b) What would the spin drift distance be at 100yds.

2. If I use a 338 LM zeroed at 500yds
a) What would the spin drift distance be at 800yds and
b) What would the spin drift distance be at 200yds.

338 LM is fired with a 290gr bullet with a BC of .880 and a Mv of 2700fps, twist is one in 7"

So gerard why do you insist on comparing two different calibers in all your examples. That will get no real comparison. It obviously takes more force to move a heavy object than a light one. If you have a loaded 18 wheeler and an unloaded 18wheeler both traveling at 60 MPH(same speed and shape). Difference in weight of 10 tons. You pull out in front of them,(Your car's force is the wind), which will be knocked off course the most by your car? The loaded one will be least affected by the impact. If you don't see that I guess we don't have much common ground to talk about.

.

Saeed,
What is an appkaee?

D Hunter,
Your analogy goes to terminal ballistics which is not what we are trying to clear up here.

Why is it OK for you to compare two bullets but not for me.

You say If one bullet weighs 200gr and another 100, the heavier will be harder to push away from it's path.

This could hardly be two bullets of the same calibre and, if they are, such a comparison will go directly to BC as the reason and not the difference in weight. The reason why I asked the questions about the .308 in Alf's post and added the 338 with a long range bullet was to establish that this simple question about wind drift has morphed into a discussion that has no relevance to the question.

I said very early in the thread: "Weight plays no role in wind drift. There are only two things that are of importance - speed and ballistic coefficient. The vertical component of wind drift is so small that it plays no role at hunting distances, unless you hunt on the other side of 500."

Between Alf and Jon A factors were brought in that cannot be calculated by the layman even if he tried. Alf admits that: "Unfortunately for me I do not have the horsepower to run these calculations, Nor the programs, from what I have read the calculations are Huge !"

Look at the second part of my post where I say: "The vertical component of wind drift is so small that it plays no role at hunting distances, unless you hunt on the other side of 500"

Alf confirms that he and Jon A have been fretting about factors that cause 25" of drift at 1000 metres with a 224 bullet and 90" of drift at 2000 metres for a 174gr .30 calibre bullet. As this spin induced drift, which is horizontal as well as vertical, increases exponentially as distance increases, what are we talking about at 500 metres with a hunting rifle that is zeroed at 200? A drift off point of aim of less than 0.5", depending on the calibre, gyroscopic stability, BC and speed.

When I stated that weight is of no concern in the addressing of wind drift and that BC and speed are the only considerations, I did not think that anyone could misconstrue that position. The clear implication is that weight is not on the same level as a factor in wind drift, as BC and speed.

Anyone who knows how to calculate BC will know that three factors go into it and that weight is one of them. Anyone who does not know how to calculate BC and simply wants to know what BC number to use in his ballistic program, does not need to be told that weight is as important as it is made out to be by some of the posts on this thread, as it is included in the BC number he uses. It confuses the issue.

We could get really technical and tell someone who loads for his 375H&H that changing the gyroscopic stability of the bullet he launches at the target, will change the angle of Alf's graph above. Therefore he must note that the horizontal and vertical component of the spin induced drift will differ by 0.015" at 100m if he changes from a 270gr soft to a 270gr solid. Unfortunately we cannot tell him by how much or in which direction because the Kray Supercomputer is down today.

This information is of great value to those shooting at 2400 yds but is it relevant to hunting inside of 500?

Alf,
Didn't those Canadians walk the shots into the target with something like over 100 rounds?

A SUMMARY OF THIS THREAD

Mike416Rigby asked:
is it normal for a heavy bullet to be moved around that much by the wind, and, can winds also impact the vertical impact of bullets on the target?

Canuck
If the wind was gusting between 10 and 15 mph, you could easily expect a half inch difference in POI between shots.

Jameister
Absolutely the wind can and does effect vertical as well as horizontal. Forget the problem of half an inch or even an inch.

butchloc
Trajectory is easy, you know how far, you know the drop, but the wind changes all the time .

Canuck
It really only makes a difference when developing loads, since if the wind is variable my group size may be more a function of the conditions than the variation in powder charge, seating depth

Gerard
Weight plays no role in wind drift. There are only two things that are of importance - speed and ballistic coefficient. The vertical component of wind drift is so small that it plays no role at hunting distances, unless you hunt on the other side of 500.

montero:
"the horizontal drift component is roughly proportional to the wind velocity and proportional to the sqaure of the range while the vertical component is roughly proportional to both the wind velocity and range".

Alf:
I respectfully disagree, MASS ALWAYS PLAYS A ROLE IN FREE FLIGHT ..................... that very "insignificant non entity of SD" plays an integral part in the physics of bullet flight !

TheBigGuy:
In short the higher the BC the less drift you will experience at the same velocity.

Alf:
BC = m/CdA or BC = m / i.d>2

DigitalDan
Two bullets with the same BC will deflect the same regardless of weight.

Jon A
for the same shape, the bullet with the higher SD will have a higher BC

TheBigGuy
I think everyone agrees the ballistic coefficient is the most telling parameter in a bullets ability to handle a cross wind.

DigitalDan
We are saddled with BC for better or worse, and when you use such a value remember it represents a practical totality of the bullets ability to overcome drag. It is convenient and it is approximate.

Jon A
What actual testing will get you is a more accurate form factor.

Alf:
if you alter weight SD changes and if SD changes BC also changes.
you can increase velocity and that would decrease wind deflection.

DigitalDan
Generally speaking increased velocity WILL reduce drift.

Gerard,
Only changes in BC and speed will affect wind drift values

Alf
SD affects BC and BC affects the effect of wind drift.

Gerard
BC greatly affects wind drift. I said so in my first post.

Alf
Does BC play a role ? Yes ! it is always true that the wind deflection of a bullet will be reduced by increasing its ballistic coefficient.

DigitalDan
In and of itself weight is a player in the calculation of BC, but not the whole picture.

TheBigGuy
Thank you this answers my question

Alf
All motion is relative. If we sit in a railway train alongside another train, we may observe from a window that the other train seems to be moving.

Gerard
BC is a factor in wind drift. Weight is a factor in BC only in the sense that you take note of what it is, in order to do the math. Increasing weight does not neccesarily increase BC

Canuck
Seems to me though, that adding weight to a bullet only lessens drift if it increases the BC.

Gerard
Logically one could say that if a bullet has weight, it will have wind drift. By the same logic, a weightless bullet will have no wind drift.

Peter
Well I thought I understood all this but I am probably mistaken.

Alf
Here I believe bullet SD comes to play in a round about way that a heavy, long, larger caliber bullet drifts less than a lighter shorter, smaller caliber bullet. The main reason for this apprently lies in the ratio of axial to transverse moment of inertia for the longer heavier bullet when compared to the light bullet.

Peter
Is that something like what you are saying?

Alf
Yes, absolutely ! Under 500 m it's not that big an issue

Gerard
You are confusing wind drift with other external ballistics such as overturning moments, yaw of repose, Magnus force and a host of other issues that are quite separate from wind drift.

DigitalDan
Alf, in your discussion with Peter regarding "drift" in calm air, I presume you are speaking of what is often referred to as Spin Drift? If so, it too is a deflection caused by Yaw of Repose.

Jon A
It's pretty silly to claim that because an equation has more than one variable that one of the variables isn't a factor in the end result.

Gerard
If weight would be a factor in wind drift, increasing weight will give a corresponding change in wind drift and decreasing it will give a corresponding and opposite change.

Jon A
In the end it's BC that matters. That is the end result, the answer to the equation one cares about for wind drift.

D Hunter
If one bullet weighs 200gr and another 100, the heavier will be harder to push away from it's path.

Jon A
That's exactly right. Ballistic Coefficient is the end result that mattters.

DigitalDan
and in the end it is BC (a measure of a bullets ability to overcome drag) that determines resistance to wind DEFLECTION.

Alf
To make the distance of spin drift less you can play with your projectile.

Gerard
What steps can I take to reduce the effect of wind on my shot placement?

Jon A
t's very hard to change the weight of the bullet and keep the form factor exactly the same,
It drifts less because it has a higher BC. BC, the end result, what matters.

Gerard
Why is this so difficult?

Jon A
The .338 has a slightly better BC but is being launched at a slightly lower velocity so many things are cancelling each other out to give similar end results.

DigitalDan
Sure the BC formula says that BC is proportional to SD, my point is that in practicality it doesn't always work that way

Gerard
Increasing or decreasing weight does not always bring a corresponding change in wind drift and trajectory.
Increasing or decreasing the BC always brings a corresponding change in wind drift and trajectory.
Increasing or decreasing the speed always brings a corresponding change in wind drift and trajectory.

Alf
I will put it to you that even if your 243 had an identical BC to the 338 and you fired both at maximum velocity in a windless environment the 338 would drift less than the 243.

Jon A
My point was BC accounts for all three equally, giving one a final answer while saving a bunch of math

High BC is of course the final answer, and IF you can get a high enough one in a light enough package, choose the lighter package as it is more efficient

Saeed
I honestly do not know why are you all making so much fuss about shooting in the wind.

Peter
I think I am learning something. Not quite sure what, just yet!

Saeed
Here is what Walter said:

"To determine how much you have to allow for the wind, stand and aim at your target - without any rest - and watch how far your aim is pushed off it. Then get down on a good rest, and aim the same distance the wind pushed on the OPPOSITE side"

Alf
Because of the fact that we zeroed the scope Spin drift in this case would have the bullet impact in the centre of the graph.

.

Alf,
Discussing stuf is fun. I get perplexed when someone says "2+2 is 4" and someone else comes along and says "Where do you come from you idiot, don't you know that (1+1)+(1+1) is four?"

I'm with Walter.

Hey guys, I've got it all figured out...I'm outa here.
Peter.

quote:

Originally posted by Gerard:
I get perplexed when someone says "2+2 is 4" and someone else comes along and says "Where do you come from you idiot, don't you know that (1+1)+(1+1) is four?"

Well, in an effort to deperplex (highly technical term ) you, this is where I was coming from:

2 apples + 2 oranges = 4 pieces of fruit. But then you said the number of apples you have has no effect on how much fruit you have, while admitting there are apples in the basket. Highly perplexing.....