Attention all ballisticians

Gene

I think Lisa said that it was gravity and time that caused a bullet to strike lower in a headwind. The bullet spent more time in the air hence gravity had a longer time to act on it. Drag is simply another way of saying the same thing. Potato, potahto.

Ray
 
2200 fps is right at 1500 mph if my rough mental cypherin is close.
So a 15mph head wind or tail wind would make almost 1% of difference.
Since Lisa was correct in her details, and also that most times all things are not equal...the drop due to head/tail wind is not a real strong consideration when compared to those other factors
 
Last edited:
I simple test you can try at home.
Take a 4X8 sheet of plywood hold it out in front of so it has a large frontal area and run into the oncoming wind for 100 yards while timing yourself.

Now repeat the test but this time let the tailwind hit the plywood.
The longer the time the lower the hit.

We need a sailboat guy here.

Cheechako you need to put down your keyboard and get driving to the 1,000 Yard Nationals.;)
Waterboy aka Lynn
 
I think that there may be a misconception of what I meant in my previous post. I stated that a bullet fired into a headwind will require more time to travel a given distance than a bullet will take to travel the same distance fired in a “no wind” situation. Therefore, the bullet fired into the headwind will drop more due to gravity having a longer period of time to act upon it.

I said nothing about drag. In my head, the increase in drag a bullet fired into a headwind experiences was a given. I apologize for not stating my belief in this.

Yes, a bullet fired into a headwind will experience increased drag over a bullet not fired into a headwind. This is the ONLY mechanism that can account for the increased time of flight. Drag is essentially the force that slows the bullet down, but…

THIS IS IMPORTANT

…drag is a factor of the shape, size, and velocity of the bullet in relationship to the ATMOSPHERE SURROUNDING the bullet—NOT IN RELATIONSHIP TO THE GROUND.

In pilot terms, it is the indicated airspeed that we are concerned with to determine the increase in drag for a headwind (or the decrease in drag for a tailwind). Unlike ground speed (which is what a chronograph will measure) it is the airspeed that matters.

Having a 10mph headwind adds other 14ish fps drag component to the bullet fired into the headwind that results in the bullet slowing down at a greater rate (The bullet essentially has to coast through more of the atmosphere to get there). It will bleed velocity faster when fired into a headwind due to increased drag. The opposite is true when fired with a tailwind.

I AM GOING TO ADD MY OWN TERM HERE, BECAUSE THIS IS HOW I THINK OF IT. IT IS NOT SCIENTIFIC, NOR IS THERE ANY BASIS FOR EVEN CONSIDERING THIS AS A REAL NUMBER, BUT IT WORKS FOR ME AND IS SIMPLE TO EXPLAIN AND TO SITE EXAMPLES (there may actually be some sciency term for this but nobody has ever told me what it is).

This term is DRAG SPEED.

I define Drag Speed as: the velocity number that is used to calculate time of flight for bullets fired into a head or tail winds.

This velocity number is derived by adding or subtracting the windspeed from the groundspeed of a bullet flying into a head or tail wind.

The simple way to compensate for this is to subtract the headwind velocity from the groundspeed velocity and calculate the time of flight to determine drop. Example: 3000 fps muzzle velocity (groundspeed) minus 14 fps headwind equals a drag speed of 2986 fps. Calculate the drop of the bullet based on 2986 fps instead of 3000 and you should be “close”.

This above paragraph is exactly what alinwa stated in his first post on this thread. Having a headwind effectively reduces the velocity of the bullet proportionally to the speed of the headwind. The opposite is mostly true of a tailwind, but the math gets squirrelly here because other factors come into play.

I do have one issue with Sierra’s statement: “the drag on the bullet would be higher, and the bullet would travel slower relative to the ground and drop more than it would if the air were still”.

I think that ground speed is the ground speed and that the bullet doesn’t actually travel “slower to the ground” it SLOWS DOWN FASTER relative to the ground.

As to the other things Gene and Ray, and Tony bring up, I’ll work on other post later with my OPINIONS.

Thanks for listening,

Lisa
 
Big Gunner said:
Glad you jumped in here. Your input is appreciated.

Lisa
Click to expand...
Thank you. I like your "Drag Speed" analogy...Easy to understand and an intuitive way to make a point. Of course it does have some brass tacks science issues with it, but anyone looking that close would go ahead and do the science in the first place. :D
 
Lisa,
"The simple way to compensate for this is to subtract the headwind velocity from the groundspeed velocity and calculate the time of flight to determine drop. Example: 3000 fps muzzle velocity (groundspeed) minus 14 fps headwind equals a drag speed of 2986 fps. Calculate the drop of the bullet based on 2986 fps instead of 3000 and you should be “close”."
I think I understand where you are going with this and as 'rule of thumb' I guess it is OK. But, (yeah I know) my thinking tells me to add the 14ish fps to the 3000 fps MV. 3014 fps velocity will slow faster (higher drag speed) than at 2986 fps do to the increased drag. Another thing I have not heard mentioned here, or if it was I missed it. Yaw factor and it effect on BC. A bullet bucking a head wind has the same force applied as if it were in Yaw. I think we can agree Yaw is a killer of BC with respect to any bullet. I some how suspect BC calculators take all this into consideration when it pukes numbers at us.

D R
 
External ballistics is a fascinating subject and we could discuss it for hours on end. In fact, I think we already have. But, this is still a Benchrest Forum and so what I'm about to say may stun some of you.

External ballistics has little to do with Benchrest shooting. :eek:

If you talk to the big kids who shoot point blank BR, I'd bet you'd be hard pressed to find even one who has ever run a ballistic chart or trajectory table for his favorite load. And with good reason. He has the best ballistic aide he will ever need. It's called the sighter target. One or two shots tells him everything he needs to know. Those holes won't lie and he doesn't have to worry about semantics or the meaning of yaw, or drag, or repose, or any of the other fancy words that we like to throw around as we show off out knowledge.

The long range Benchrest shooter (of which I R 1), on the other hand has a brief case full of ballistics charts, one for each load, for each range that he will be shooting at, for every elevation from sea-level to Denver, and for every weather condition from Williamsport to Reno. But, once he establishes his dead-air zero those charts go back into the briefcase. Like the point blank guys, he fires his sighters and hopes conditions will not change before the record target goes up. I can't remember a time when I saw a 1000 yard shooter consulting his charts in the middle of a string or between strings.

So, keep the ballistic discussions going but don't lose sight of the goal.

JMHO

Ray
 
Big Gunner said:
I do have one issue with Sierra’s statement: “the drag on the bullet would be higher, and the bullet would travel slower relative to the ground and drop more than it would if the air were still”.

I think that ground speed is the ground speed and that the bullet doesn’t actually travel “slower to the ground” it SLOWS DOWN FASTER relative to the ground.


Lisa
Click to expand...

Lisa,
I think Sierra is talking about the horizontal component of velocity, which is slower, not the vertical component. If the bullet decelerates at a greater rate, then it must accumulate an increasing deficit in velocity relative to the no wind case.

Cheers,
Keith
 
Doing the science

I think that doing the science is a big part of the problem for this type of thread.

Lots of us can do the actual math to figure out each and every aspect to determining the path of the bullet.

Adding it all up to mean something is where it all gets confusing.

Most everyone reading these posts has the ability to apply the formulas necessary to calculate drop, drift, yaw, etc, individually. Calculating them in relationship to one another is damn hard.

Even if you do it, it doesn't work out. I can gaurantee that the answer you come up with figuring it all out on a piece of paper at the kitchen table is going to be different than what happens on a piece of paper attached to the target board.

This is all fun to talk about, but in the scheme of things, all that really matters is what happens on the target.

I am INTERESTED in the mechanism of why these things happen, I must KNOW that they do in order to shoot well.

Sighters are great!

Lisa
 
I just recently found this thread and honestly haven't read every post, just the last few, and I just have one question:

Lisa,
Will you be my internet girlfriend ;)
 
Brian,

You can't have her just to yourself. Lisa is the sweetheart of the whole dang rodeo.

Greg
 
Bryan! My Man!!!

Delighted to hear from you; thanks for joining us! :D

Wow! Bryan Litz. This is our lucky day gang. :)

On a more serious note,,,,

Now listen, you and Greg Culpepper lay off trying to steal my girlfriend Lisa. :mad: With that understood,, proceed. :mad: :) :D
 
Hey Bryan, I hope you will scroll down to a thread entitled, "For You Ballisticians" started by Richard Fast (Model 14) It was most interesting. Hope you can proof read it for us and see if we missed anything. Thanks

Gene Beggs
 
Cheechako said:
Richard & Gene

Let me quote directly from William McDonald and Ted Almgren, ballisticians at Sierra Bullets:

". . . in the case of a headwind acting alone and blowing from the target toward the shooter, the speed of the bullet relative to the air would be greater than it would be if the air were still. Then, the drag on the bullet would be higher, and the bullet would travel slower relative to the ground and drop more than it would if the air were still. On the other hand, for a tailwind acting alone and blowing from the shooter toward the target, the speed of the bullet relative to the air would be less than it would be if the air were still. Then, the drag on the bullet would be lower, and the bullet would travel faster relative to the ground and drop less than it would if the air were still. . ."

Calculating the effect of head and tail winds is basic high school math. Not a lot of room for misconceptions. :rolleyes:

What am I missing???:confused::confused: Or, maybe a better question would be, what are McDonald & Almgren missing?

Ray
Click to expand...

Ray,

Knowing there will be a hue and cry of momentous proportions, the above statement by McDonald & Almgren is incorrect!

From an observer on the ground standpoint it is true that the speed of the bullet relative to the air is greater when a headwind is blowing. But the drag on the bullet has nothing to do with what someone (or an instrument) on the ground observes.

Drag force on the bullet is only generated by the air velocity as seen by the bullet. Since the bullet is not connected to the ground it does not feel a headwind.

You observe the effects of the headwind by measuring bullet speed relative to the fixed ground. If you want the actual bullet speed relative to the air around it you must subtract the value of the headwind.

Actual bullet speed in the air surrounding it determines the drag force on the bullet.What Lisa gave you was a way of looking at headwinds as a drag producer but it will not work to compute the actual drag forces acting on the bullet, unless you subtract out the value of the headwind.

As I stated before:
Drag Force (acting to decelerate the bullet) =
1/2 *(wind velocity measured at the bullet not the ground)^2 * air density
*drag coefficient (mainly a function of shape).

What Lisa gave you was a layman's way of explaining the effect of a headwind, not the actual calculation methods for drag.

I stand by my statement that your saying that a headwind causes an increase in drag is incorrect.

Headwind causes an increase in the time it takes the bullet to reach the target, and therefore it drops more due to gravity. The drag force on the bullet has nothing to do with the headwind.

Richard
 
model14 said:
... The drag force on the bullet has nothing to do with the headwind.

Richard
Click to expand...

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
 
model14 said:
Ray,Knowing there will be a hue and cry of momentous proportions, the above statement by McDonald & Almgren is incorrect!Richard
Click to expand...

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
 
Richard,

and everyone else.

I apologize for not being able to state clearly what I can see in my head. Any confusion here is my fault.

I thought that I had explained that the ground speed of the bullet is irrelevant to the drag on a bullet, and that it was solely dependant on the atmosphere surrounding the bullet.

Additionally, I thought that I had explained that it was the airspeed of the bullet that determined drag, not it's speed relative to the ground. A chronograph measures groundspeed, not airspeed.

I really think that Richard and I are on the same page, I'm just unable to explain in an understandable manner what I see in my head.

Let me ask this question. Richard, using the formula you so kindly wrote above, is there an increase in the drag force on the bullet if it is fired into a 100mph headwind, versus if were fired into a 100 mph tailwind?

I will try and find another way to explain my opinion.

Thanks,

Lisa
 
http://www.biggameinfo.com/index.aspx?page=/balcalc.ascx
This is a cute little calculator to play with on this subject.
I took the default numbers and looked at what a 15mph (20fps) headwind and similar tailwind would do. Comparing the remaining velocity downrange.
I made what I would consider a valid (short duration) assumption and looked at how much velocity was lost in 100 yards between a shot at 3020fps (20fps headwind) vs 3000 fps (calm), vs 2980 fps (20 fps tailwind) (subtracting remaining vel from MV - treating MV as initial airspeed and remaining vel also as airspeed at range)
the head wind scenario lost 1fps more than it did in calm and 2 fps more than in a tailwind over the course of 100 yards.
At 500 yards the difference was up to 9 fps between headwind vs tailwind.
Not a lot of difference, in fact a lot of online calculators ignore headwind/tailwind in the velocity calculations.
For rimfire curiosity I used 1100, 1080, and 1060fps with a BC of 0.12
Which resulted in a 10fps increased loss in a head wind vs a 9fps decreased loss in a tailwind.
 
Last edited:
It ain't as simple as it looks; is it? :eek:

Some believe a headwind of 20 fps results in greater drag on the bullet all the way to the target while others say it does not.

Some are confused about the difference between airspeed and groundspeed.

Me? Well, I don't know much but 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.

During my 22 years of involvement with benchrest, I have shot only 100 and 200 yard group; mostly with a 6PPC. I have no experience at 600 and 1000 yards, but this is what I have observed.

1. A ninety degree crosswind from right to left drifts my bullets left and up; a ninety degree crosswind from left to right drifts my bullets right and down.

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

Bryan Litz can help us if anyone can. Hope he has the time.

Later



Gene Beggs
 
You must log in or register to reply here.
Back
Top