For you ballisticians.

[tobybradshaw]

You are stating that a momentary crosswind doesn't have the ability to permanently alter the direction of the bullet with respect to the ground.

That's right.

For me, this is easier if you think of an aerodynamically stable object moving at constant speed (thanks to Greg Culpeper and Gene), starting at one point and aiming for a distant "target." When the object hits the momentary crossflow (wind, water, whatever) it turns into the relative flow (a necessary outcome of being "stable") at an angle equal to the arctan(crossflow component/downrange component) and a downrange component equal to sin(crossflow component/initial velocity).

Seen from above, the boat/plane is nose-into-the-relative-flow, but its trajectory is still straight towards the original "target" (even though its nose is no longer pointed in that direction). The downrange component of velocity (towards the target) is now reduced, because some of the constant speed is "used up" to "counter" the crossflow component vector.

In the extreme case where the crossflow velocity is equal to the boat/plane's constant speed, as seen from above the boat/plane is stationary, pointed 90 degrees from the initial trajectory. If the crossflow declines just a little, the boat/plane will nose slightly in the direction of the target (but still not pointed directly at it), and begin to creep along the straight line from the starting point to the target.

What happens if we throttle back on the boat/plane for a bit while it is in the crossflow? As seen from above, the boat/plane now moves backwards in the direction of the relative flow, aligned with the long axis of the boat/plane. So now it is moving backwards at angle to its original line of departure, and deflecting down-flow relative to the target, but it still has a component of velocity pointed in the direction of the target.

The component of velocity in the direction of the target guarantees that the boat/plane will eventually emerge from the crossflow and back into the "calm" condition it started in. As soon as the boat/plane emerges back into the calm condition, its nose re-orients into the new relative flow, which is parallel to the starting direction, but the boat/plane has been displaced down-flow because it decelerated while in the crossflow.

BTST, when the bullet is relinquished by the crosswind it HAS a side vector, what force causes it to resume its old course?

Drag along the line between the bullet's center of pressure and center of mass, which aligns itself with the relative wind. When the center of pressure moves (because of a change in relative wind direction) the bullet's long axis rotates relative to the ground.

Toby Bradshaw
baywingdb@comcast.net

 

[tobybradshaw]

The component of velocity in the direction of the target guarantees that the boat/plane will eventually emerge from the crossflow and back into the "calm" condition it started in. As soon as the boat/plane emerges back into the calm condition, its nose re-orients into the new relative flow, which is parallel to the starting direction, but the boat/plane has been displaced down-flow because it decelerated while in the crossflow.

Sorry to follow my own post, but it would have been more complicated (and perhaps tackier) to edit the old post instead.

In thinking about the boat/plane analogy in the "crossflow at 500-600yd" scenario, it seems to me that the trajectory going in and the trajectory coming out of the crossflow are parallel (on the same straight line, in fact) if the boat/plane's speed is constant (which is how I had been thinking about it).

But if Al's and Tony's point is that a bullet (constantly decelerating) goes into the crossflow (500yd) at a higher velocity than it emerges (600yd), the nose angle change (relative wind direction) is less going in than coming out, so the bullet does not emerge from the crossflow parallel to the line of departure, but instead it is pointed slightly downwind.

So, I admit defeat on the "no permanent change in trajectory" claim. Al and Tony were right, at least for decelerating objects.

Damn, I hope crow tastes better than it smells.

Toby Bradshaw
baywingdb@comcast.net[/QUOTE]

 

[mks]

when changing targets and taping up backers, often bullets pass through both the target and backer in what appears to an angle downward and right. I don't ever remember seeing a hole that semed to be angling toward the left. I am thinking all the while when reading this, some of what I see on the paper would be in direct contradiction to the science. Perhaps I just don't understand what I am reading here or there are extenuating circumstances.

Pete,
The downward angle is due to the gravity-induced downward trajectory of the bullet and the rightward angle is due to the yaw of repose for a right hand spinning bullet. With no crosswind, right spinning bullets drift right like a slice from a right handed golfer. (A golf ball doesn't turn right for the same reason as the bullet. I'm just trying to make the description more visual.)

Cheers,
Keith

 

[glp]

Pete

when changing targets and taping up backers, often bullets pass through both the target and backer in what appears to an angle downward and right. I don't ever remember seeing a hole that semed to be angling toward the left. I am thinking all the while when reading this, some of what I see on the paper would be in direct contradiction to the science. Perhaps I just don't understand what I am reading here or there are extenuating circumstances.

we'll shoot some bullets into a 100 yd target with my M1917 Enfield sometime...left hand twist.

 

[tobybradshaw]

This would be so much easier with a blackboard.

The scenario:

BIB 95gr FB BC=0.435
muzzle velocity=3000ft/sec
crosswind @ 3'oclock @ 10mi/hr (15ft/sec) from 500-600yd only

At 500yd the bullet is going 1964ft/sec. When it hits the 15ft/sec crosswind the bullet turns into the wind [the point turns to the right] by arctan(15/1964)=0.44degrees.

The nose angle continues to increase until the bullet has reached 600yd, at which time it is going 1783ft/sec and has a nose angle of 0.48degrees. It has been deflected downwind (left) about 1.2 inches between 500-600yd.

Upon entering the "calm" air past 600yd, the bullet's nose turns leftward into the relative wind by arctan(15/1783), which is 0.48degrees. So, the bullet is now pointing 0.04degrees to the left of the line upon which it entered the crosswind, and thus continues to diverge downwind from the original line of departure from the bore, which amounts to about 2.5 inches leftward displacement for every 100yd thereafter (3600inches/100yd*tan(0.04degrees)) for a grand total of about 11.2 inches at 1000yd (of which only a little over an inch happened during the "push").

Resolved: I will shoot more and do less typin' and figgerin'.

Toby Bradshaw
baywingdb@comcast.net

 

[Gene Beggs]

Toby,, WHOA! Don't be so quick to,,

Sorry to follow my own post, but it would have been more complicated (and perhaps tackier) to edit the old post instead.

In thinking about the boat/plane analogy in the "crossflow at 500-600yd" scenario, it seems to me that the trajectory going in and the trajectory coming out of the crossflow are parallel (on the same straight line, in fact) if the boat/plane's speed is constant (which is how I had been thinking about it).

But if Al's and Tony's point is that a bullet (constantly decelerating) goes into the crossflow (500yd) at a higher velocity than it emerges (600yd), the nose angle change (relative wind direction) is less going in than coming out, so the bullet does not emerge from the crossflow parallel to the line of departure, but instead it is pointed slightly downwind.

So, I admit defeat on the "no permanent change in trajectory" claim. Al and Tony were right, at least for decelerating objects.

Damn, I hope crow tastes better than it smells.

Toby Bradshaw
baywingdb@comcast.net

[/QUOTE]



,,,chow down on a big helping of crow. You're not wrong; there is something that perhaps you have not considered. Let me explain.

First, I must congratulate Alinwa on a brilliant piece of work in coming up with this little brain teaser. Al, you have come a long way since our discussions began over on the 1000 yard forum some time ago. How long now? Time flies; it's probably been longer than I remember.

Yes sir, Al,,one must have a very good understanding of how wind affects bullets to even be able to visualize and present this scenario. Good on ya' man!

Now down to business.

By now, most everyone agrees (except Sierra ) that bullets turn their nose into a crosswind in order to streamline themselves to the relative wind, but just how much do they turn; how much wind correction or 'crab' do the bullets establish?

Answer? It depends on the airspeed (velocity) of the bullet and the crosswind component. Let's take for example two bullets; identical in every way except one is going 2500 fps when it encounters the 10 mph crosswind at 500 yards, the other is going 3000 fps. Which bullet will make the biggest heading change in order to streamline itself when it encounters the crosswind at 500 yards? Sure,, the slower one; the one that is going 2500 fps.

Now,, with what you have learned in the previous paragraph, apply that to the scenario about the bullet entering the crosswind at 500 yards at one speed and exiting at 600 yards into a calm condition at a slower speed. The wind correction angle established at the higher airspeed upon entering the crosswind will be less than that at exit at 600 yards at the slower airspeed; one cancelling out the other so to speak, and the bullet resumes its flight to the target at 1000 yards on a ground track parallel to that of the first 500 yards.

Toby, mull this over in your mind for a little while and you will see what I'm talking about and be able to explain it much better than I have.

Gene Beggs



A few minutes later,,,MMMMM!!, Let's see, NO I'm wrong; let me think about this a bit. Al, you may have me backed into a corner. I may be lost. I'll get back to you; How's that?

 

[tobybradshaw]

Now,, with what you have learned in the previous paragraph, apply that to the scenario about the bullet entering the crosswind at 500 yards at one speed and exiting at 600 yards into a calm condition at a slower speed. The wind correction angle established at the higher airspeed upon entering the crosswind will be less than that at exit at 600 yards at the slower airspeed; one cancelling out the other so to speak, and the bullet resumes its flight to the target at 1000 yards on a ground track parallel to that of the first 500 yards.

Hi Gene. I ran the numbers and they don't cancel out -- the slower bullet turns more coming out than the (same) faster bullet did going into the "band" of crosswind.

Of course, I could be wrong (again!).

Toby Bradshaw
baywingdb@comcast.net

 

[tobybradshaw]

At 500yd the bullet is going 1964ft/sec. When it hits the 15ft/sec crosswind the bullet turns into the wind [the point turns to the right] by arctan(15/1964)=0.44degrees.

The nose angle continues to increase until the bullet has reached 600yd, at which time it is going 1783ft/sec and has a nose angle of 0.48degrees. It has been deflected downwind (left) about 1.2 inches between 500-600yd.

Upon entering the "calm" air past 600yd, the bullet's nose turns leftward into the relative wind by arctan(15/1783), which is 0.48degrees.

DAMMIT! At 600yd, still in the crosswind, the bullet's nose is pointing 0.48degrees to the right. The leftward movement after 600yd is also 0.48 degrees, making the net departure angle 0 degrees, i.e., parallel to the initial trajectory.

So, THIS TIME, I'm saying that Gene is right (as usual), that they cancel out.

Resolved AGAIN: I will shoot more and do less typin' and figgerin'.

Where is the emoticon for SON OF A B****!!!

Toby Bradshaw
baywingdb@comcast.net[/QUOTE]

 

[Gene Beggs]

Hi Gene. I ran the numbers and they don't cancel out -- the slower bullet turns more coming out than the (same) faster bullet did going into the "band" of crosswind.

Of course, I could be wrong (again!).

Toby Bradshaw
baywingdb@comcast.net

No Toby, you're probably right , but let's see,,,

,,we're in this bullet cruising along for 500 yards in a no wind condition and suddenly encounter a 10 mph crosswind from left to right at the 500 yard point; airspeed (oops) 'er, velocity is showing 2200 fps. Upon entering the crosswind, we feel a hard bump on the left side of the bullet and the nose yaws to the left and settles down a bit left of the original heading. We note that velocity is slowly but steadily decreasing and we are drifting slightly right of centerline.

At the 600 yard line, with velocity slowing thru 2000 fps, we feel a hard bump on the right side of the bullet and the nose yaws to the right,, FREEZE! That's right, freeze the motion and let's talk about this a bit.

Here we sit in this bullet with the nose pointed off to the left slightly when we entered this motionless column of air that lies between us and the target board. Since our bullet must now streamline itself with the motionless airmass, how far must it turn to the right to do this? That's right; whatever crab it had going in.

Make sense? Now what do you think?

Gene Beggs

 

[tobybradshaw]

Make sense?

Gene Beggs

Yes!

Now I'm down to just one helping of crow, courtesy of Boyd and Sierra.

Toby Bradshaw
baywingdb@comcast.net

 

[Gene Beggs]

Eating crow? Nah,, I don't think so!

Yes!

Now I'm down to just one helping of crow, courtesy of Boyd and Sierra.

Toby Bradshaw
baywingdb@comcast.net

Toby, I don't think you're gonna' be eating crow any time soon. The information in the Sierra manual about wind drift is wrong; the nose of a bullet turns INTO a crosswind.

I must say, the folks at Sierra are great people and very knowledgeable; they will do whatever is right.

Gene Beggs

 

[tobybradshaw]

Toby, I don't think you're gonna' be eating crow any time soon. The information in the Sierra manual about wind drift is simply wrong. The nose of a bullet turns INTO a crosswind.

Gene Beggs

Boyd's claim was that "experts disagree." Now, I think we could make a good case against the "expertise" of the Sierra ballisticians, but Boyd is still going to get a box of bullets.

Physicist J.J. Thomson said it best (about golf balls, not bullets, but the message is the same):

" ... a golf ball, which is, in reality, the most prosaic of things, knowing while in the air only one rule of conduct, which it obeys with unintelligent conscientiousness, that of always following its nose."

Toby Bradshaw
baywingdb@comcast.net

 

[Butch Lambert]

Toby and fellow buddies, while I have your attention do you have any idea of the possible vertical spread of a 300 win mag using a Nosler Accubond 200 grain bullet at 2980FPS with an ES of 50fps at 1000 yds?
Butch

 

[Gene Beggs]

Yes, I read the piece on golf balls,,,

Boyd's claim was that "experts disagree." Now, I think we could make a good case against the "expertise" of the Sierra ballisticians, but Boyd is still going to get a box of bullets.

Physicist J.J. Thomson said it best (about golf balls, not bullets, but the message is the same):

" ... a golf ball, which is, in reality, the most prosaic of things, knowing while in the air only one rule of conduct, which it obeys with unintelligent conscientiousness, that of always following its nose."

Toby Bradshaw
baywingdb@comcast.net

,,,most interesting!

Life used to be so simple. When we were kids, we had so much fun playing with golf balls, baseballs, tennis balls, you name it. We shot our BB guns into strong crosswinds and watched the little copper colored projectiles arc downwind. We thought we knew it all. Now we discover we didn't know squat!


Later,

Gene Beggs

 

[Tony Shankle]

This would be so much easier with a blackboard.

The scenario:

BIB 95gr FB BC=0.435
muzzle velocity=3000ft/sec
crosswind @ 3'oclock @ 10mi/hr (15ft/sec) from 500-600yd only

At 500yd the bullet is going 1964ft/sec. When it hits the 15ft/sec crosswind the bullet turns into the wind [the point turns to the right] by arctan(15/1964)=0.44degrees.

The nose angle continues to increase until the bullet has reached 600yd, at which time it is going 1783ft/sec and has a nose angle of 0.48degrees. It has been deflected downwind (left) about 1.2 inches between 500-600yd.

Upon entering the "calm" air past 600yd, the bullet's nose turns leftward into the relative wind by arctan(15/1783), which is 0.48degrees. So, the bullet is now pointing 0.04degrees to the left of the line upon which it entered the crosswind, and thus continues to diverge downwind from the original line of departure from the bore, which amounts to about 2.5 inches leftward displacement for every 100yd thereafter (3600inches/100yd*tan(0.04degrees)) for a grand total of about 11.2 inches at 1000yd (of which only a little over an inch happened during the "push").

Resolved: I will shoot more and do less typin' and figgerin'.

Toby Bradshaw
baywingdb@comcast.net

10.8" at 1000 Toby. But I still love ya!

 

[Tony Shankle]

Toby and fellow buddies, while I have your attention do you have any idea of the possible vertical spread of a 300 win mag using a Nosler Accubond 200 grain bullet at 2980FPS with an ES of 50fps at 1000 yds?
Butch

Assuming the 50 fps of ES is half up and half down (3005 to 2955)...

The 3005 fps shot results in a -246.3 or 23.50 moa needed correction.
The 2955 fps shot results in a -256.3 or 24.50 moa needed correction.

Spread on target is 10.0 inches.

 

[alinwa]

No Toby, you're probably right , but let's see,,,

,,we're in this bullet cruising along for 500 yards in a no wind condition and suddenly encounter a 10 mph crosswind from left to right at the 500 yard point; airspeed (oops) 'er, velocity is showing 2200 fps. Upon entering the crosswind, we feel a hard bump on the left side of the bullet and the nose yaws to the left and settles down a bit left of the original heading. We note that velocity is slowly but steadily decreasing and we are drifting slightly right of centerline.

At the 600 yard line, with velocity slowing thru 2000 fps, we feel a hard bump on the right side of the bullet and the nose yaws to the right,, FREEZE! That's right, freeze the motion and let's talk about this a bit.

Here we sit in this bullet with the nose pointed off to the left slightly when we entered this motionless column of air that lies between us and the target board. Since our bullet must now streamline itself with the motionless airmass, how far must it turn to the right to do this? That's right; whatever crab it had going in.

Make sense? Now what do you think?

Gene Beggs

You'se guys are getting close but still figgering planes and not decellerating projectiles

Let's fuh'GEDDABOUT the part of the trajectory before the stream of crosswind at 500-600..... we just pick up the bullet crabbing across the stream, it's DEFINITELY on a downwind course and fairly crabbed over..... and sl o o w i n g as it goes....

Now, when it pops out into clear air on the other side it does NOT "resume course"....... it renegotiates a new velocity which retains some of it's divergence.... not ALL, but some of it.


I'll try to draw a picture since this is the ONE salient point which puts about three years argument into perspective!

This goes back to months ago with "you and me on two sides of the ribber" Gene

Let's Get 'Er Done Eh!!!!

LOL


al

 

[alinwa]

Toby and fellow buddies, while I have your attention do you have any idea of the possible vertical spread of a 300 win mag using a Nosler Accubond 200 grain bullet at 2980FPS with an ES of 50fps at 1000 yds?
Butch

Yuppers Butch, da' man's right

FIVE FEET PER SECOND equals about an inch at 1000yds!!!! 50fps = 10"


THIS is why I weigh to the kernel and THIS is why "SD" and all derivatives thereof is rotten fruit........ you can put nine bullets into 2" but you get ONE SLOW ONE and your group is a foot deep, for a 12" group.


bummerdealdude!


Two statisticians (physicists, mathematicians, CPA's, insert favorite epithet here) are attempting to hit a grapefruit at 100yds......

1st shot is 10ft to the right and 12" low.........


(figger figger, mutter mutter)


2nd shot is 10ft LEFT and 12" HIGH........



High fives all-round, much backslapping and fistbumping....... "ZERO deviation! we NAILED that sucker eh!!! THAT is ONE DEAD MELON, ABsolutimally DEAD ZERO.........




THAT fruit is a statistic!


Shucks, you can hit your melon and eat it too!

with statistics





al

 

[Boyd Allen]

Hey Gene, read paragraph four

http://www.exteriorballistics.com/ebexplained/articles/article2.pdf

 

[alinwa]

http://www.exteriorballistics.com/ebexplained/articles/article2.pdf

hmmm

cool link.

One thing that bugs me though about the Sierra guys is that they use stuff like "rising arc" and "summit" and "falling arc" of trajectory when in reality a bullet just DROPS from the line of the bore. Later in their explanation they note that the yaw of repose is different on the "rising side" than the "falling side"....


?????


howso?



Initial or departure angle in flatfire diagrams is irrelevant and teachers should just get rid of "rising" and "falling" IMO because it's confusing. The bullet isn't "plowing up through the air" and then "falling down'....

well..........

TOTALLY off subject



LOL


al