Wind Quiz

[Canadian bushman]

I'm ok with agreeing to disagree. I don't think there is a shooter alive that can shoot the difference at long range and probably not at 100 either. ..but that's just me. I simply think the value of this scenario is overrated and often overstated.

I can respect that

 

[Joe Salt]

Our first 1000 yard match had 20 MPH winds on Sunday and there were some of us that done mediocre. There was a right to left wind and I shot on bench 3. I shot a 10.4 inch group with a 92 score all in the blue. There were some top shooters in my relay, so I was happy to do that good. On Saturday I got a wind report, but my load for the L.G. was to slow. That was because I used my new LabRadar during the match. The shots started in the Nine ring and went just out of the scoring. Too bad that labRadar doesn't give you wind speed.

Joe Salt

 

[fredo]

Yes, thats what I'm saying. I think given the example used in this thread, negligible is a good way to describe it.

The point of the thread is to show the following:

The sooner a lateral wind imparts force upon a bullet during it's flight path, the greater the amount of deflection said wind will have on target, downrange.

Also, the longer said wind imparts lateral force upon a bullet will increase the degree of that deflection.

Getting off of a flat range & relying on wind flags all over the place, and shooting on uneven terrain, over/across valleys, etc... will show how ignoring/marginalizing wind close to shooter position will eat your lunch at distance.

Wind is water. I start my wind call by paying attention to close wind, first, and work on out from there. Idea is to try to make sense of how wind downrange will affect bullet flight AFTER the close wind has already acted upon the bullet & deflected its trajectory...

 

[Joe Salt]

Fredo I was watching the vapor trail while some of the guys were shooting and the bullets had to go further at about mid range to be able to stay on paper. So I don't now exactly what you are looking for but the bullet has to be pointed into the wind enough or you are not going to hit what you are aiming at. And I'm sure down range the wind has some affect, but it looks like a big curve. So I say wind from the bench out to mid range.

Joe Salt

 

[fredo]

I know what you're saying about watching trace, Joe.
I shoot alone often, and in the last few years, have been videoing some shooting sessions to catch trace on camera. It is both cool and informative to watch, from directly behind shooting position...

Was posting to reiterate that marginalizing the affect of close range wind is not conducive to making a good first round hit from a 'dialed in' wind call.
From a field position, without the aid of wind flags at pre-determined distances, thinking of wind flowing like water over the terrain allows the shooter feedback to make a determination. That's a moot point for square ranges with flags, but valid to the topic, nonetheless...

 

[338 Mollett]

Good Post! sorry to enter the conversation so late. Say a man is rowing a boat across a river the first half has current witch takes him down stream.The second half has zero current thus the canoe has to straighten out on it's path.I think the same happens to a bullet.Is the wind going to change the direction of the bullets nose in the first 500 yd.no wall scenario ?

 

[Victor Hanna]

shooter b

 

[Joe Salt]

You can look at flags all you want at are range, but you will never be dead on. If you are lucky you will maybe shoot 12" in a wind like we had Sunday. All I can tell you if your rifle won't shoot through it, better get one that will. If you have the wind picking up and letting off, your in trouble no matter were you shoot.
Victor at our range if you are on bench 1 and the wind is blowing from left to right you have a better chance of winging because the trees block the wind for about 400 yards. Look at the results on www.pa1000yard.com between L.G. and H.G. Saturday the wind blew from left to right, then Sunday from right to left.

Joe Salt

 

[gunsandgunsmithing]

I certainly don't have all the answers and can't solve the world's problems...Far from it, but let me ask a question and say a few words to ponder on this subject. Remember, I'm no expert and there are people that are much more qualified than I..but, my questions is, why does the wind at one location have more effect than at another?? It has to be drag and time. There is no other explanation.

That brings another question...What if the bullet lost no speed at range? Would it matter where the wind was? I think not.

So, the answer must be contingent upon drag and time. With speed comes drag, so the faster the bullet is going, relative to time, must generate MORE drag. With more drag, do we have more drift? I say yes.

Also, BC is relative to drag and changes somewhat with speed. So, if we fire a .35 G7 BC bullet at 3000fps, it must also have a calculable TOF at all ranges. It does.

For grins, I used Bergers ballistic app and I used these same numbers, 3000fps at the muzzle and a G7 of .35.
At 500 yards the bullet was going 2364fps and was 11.35 inches drifted in 10 MPH crosswind. I then used the same bullet at 2364fps muzzle velocity, and at 500 yards the bullet had slowed to 1811fps but drifted 16.19 inches.
So, is there something that I'm missing or something that the program misses, as this clearly implies more drift at the far end with lower velocity than at the front end with 3000fps at the muzzle?

 

[338 Mollett]

Great thread guy's a lot of good thinking between beer's on this cheers!

 

[Marksman63]

I certainly don't have all the answers and can't solve the world's problems...Far from it, but let me ask a question and say a few words to ponder on this subject. Remember, I'm no expert and there are people that are much more qualified than I..but, my questions is, why does the wind at one location have more effect than at another?? It has to be drag and time. There is no other explanation.

That brings another question...What if the bullet lost no speed at range? Would it matter where the wind was? I think not.

So, the answer must be contingent upon drag and time. With speed comes drag, so the faster the bullet is going, relative to time, must generate MORE drag. With more drag, do we have more drift? I say yes.

Also, BC is relative to drag and changes somewhat with speed. So, if we fire a .35 G7 BC bullet at 3000fps, it must also have a calculable TOF at all ranges. It does.

For grins, I used Bergers ballistic app and I used these same numbers, 3000fps at the muzzle and a G7 of .35.
At 500 yards the bullet was going 2364fps and was 11.35 inches drifted in 10 MPH crosswind. I then used the same bullet at 2364fps muzzle velocity, and at 500 yards the bullet had slowed to 1811fps but drifted 16.19 inches.
So, is there something that I'm missing or something that the program misses, as this clearly implies more drift at the far end with lower velocity than at the front end with 3000fps at the muzzle?

You miss that bullet drifts according a non linear wind/speed correlation coefficient

 

[Mozella]

....... snip........
At 500 yards the bullet was going 2364fps and was 11.35 inches drifted in 10 MPH crosswind. I then used the same bullet at 2364fps muzzle velocity, and at 500 yards the bullet had slowed to 1811fps but drifted 16.19 inches.
So, is there something that I'm missing or something that the program misses, as this clearly implies more drift at the far end with lower velocity than at the front end with 3000fps at the muzzle?

Yes, you did miss something. Your test shows that a slower flying bullet will drift more than a faster one in the same wind over 500 yards; no surprises there. But the quiz was at a range of 1000 yards. So assuming no wind for the first half, your drift of 16.19 caused by the wind in the last 500 yards would be correct, or nearly correct.

But remember, the bullet which has the wind only in the first 500 yards will drift 11.35" in the first half of the flight, but it will retain much of that established drift for the second 500 yards (in spite of no wind for the last 500 yds) and therefore the shift in POI will be more than the 16.19" of the first example. In other words, it will be 11.35" PLUS the change in POI caused by the retained drift established by the close wind and that number will be greater than 16.19".

Of course it's not quite that simple because bullets are known to turn in cross winds, the angle of attack changes as the bullet arcs toward the target, and there are spin drift and Coriolis effects to be considered, but these factors are relatively small compared to the gross wind drift. So the exact change in POI may be a little bit different from this example. However, the concept that near wind is more important is valid.

 

[Mozella]

Yes, you did miss something. Your test shows that a slower flying bullet will drift more than a faster one in the same wind over 500 yards; no surprises there. But the quiz was at a range of 1000 yards. So at the risk of beating a dead horse which has been already pounded into mush earlier in this thread, assuming no wind for the first half, your drift of 16.19 caused by the wind in the last 500 yards would be correct, or nearly correct.

But remember, the bullet which has the wind only in the first 500 yards will drift 11.35" in the first half of the flight, but it will retain much of that established drift for the second 500 yards (in spite of no wind for the last 500 yds) and therefore the shift in POI will be more than the 16.19" of the first example. In other words, it will be 11.35" PLUS the change in POI caused by the retained drift established by the close wind and that number will be greater than 16.19".

Of course it's not quite that simple because bullets are known to turn in cross winds, the angle of attack changes as the bullet arcs toward the target, and there are spin drift and Coriolis effects to be considered, but these factors are relatively small compared to the gross wind drift. So the exact change in POI may be a little bit different from this example. However, the concept that near wind is more important is valid.

 

[gunsandgunsmithing]

Yes, you did miss something. Your test shows that a slower flying bullet will drift more than a faster one in the same wind over 500 yards; no surprises there. But the quiz was at a range of 1000 yards. So assuming no wind for the first half, your drift of 16.19 caused by the wind in the last 500 yards would be correct, or nearly correct.

But remember, the bullet which has the wind only in the first 500 yards will drift 11.35" in the first half of the flight, but it will retain much of that established drift for the second 500 yards (in spite of no wind for the last 500 yds) and therefore the shift in POI will be more than the 16.19" of the first example. In other words, it will be 11.35" PLUS the change in POI caused by the retained drift established by the close wind and that number will be greater than 16.19".

Of course it's not quite that simple because bullets are known to turn in cross winds, the angle of attack changes as the bullet arcs toward the target, and there are spin drift and Coriolis effects to be considered, but these factors are relatively small compared to the gross wind drift. So the exact change in POI may be a little bit different from this example. However, the concept that near wind is more important is valid.

Please quantify the term retained drift, as used in your example. How much of this retained drift is, well....retained?

 

[fredo]

Here's a (not so) quick video to show how 'close' wind and broken terrain factors into a making a call.

In this spot, I'm shooting over a valley where the terrain falls away, down & to the right of the shooting position. This causes close range wind to 'flow' down that hill, which has a measurable affect downrange.

The wind on the far side of the valley is cookin' L<--<--<--R, as you can see via vegetation in the video. This is nearly opposite the direction of the close range wind that 'flows' like water down the valley...

The result? My wind call (to hold ~0.7 mil right) is barely 1/2 of what would be required if I only factored in the far wind, nearer the target.

Watch the bullet trace @ ~55 second mark in the video, and you can see the far wind begin to act on the bullet, but only at the far end of its trajectory. The 215Hybrid barely 'curls' into the center of the plate in the last few hundred yards...

Cartridge is a .30-338Norma Improved, 215Hybrid @ 3145fps, 1300ASL

http://vid12.photobucket.com/albums...C-6942-45FF-BDC3-BFFE7AF32F21_zps6hptce0g.mp4

If close range wind were ignored, a hold for a 15-20mph right to left crosswind would be nearer to 1.8 mils. At 990 yds, that 1.0 mil difference in wind call equates to almost 3 feet of horizontal. IE, a very obvious MISS!

Even though the close range wind 'flow' is not near as strong, the fact that it deflects the bullet so early on in its flight has a significant effect, downrange...

 

[Mozella]

Please quantify the term retained drift, as used in your example. How much of this retained drift is, well....retained?

I don't know. The bullet experiencing the near wind (the first 500 yards) will follow a curved arc and and halfway down the range when the wind stops, it will be traveling in a different direction from when it left the barrel. I'm not going to attempt to calculate the amount of angular difference, but I think it's obvious that the flight path at the end of the first 500 yards is no longer parallel to the barrel. That being the case, it will continue to diverge from the POA during the second 500 yards even though the wind has stopped.

 

[Joe Salt]

fredo To hit that target I believe we are talking the same. The bullet has to start out being shot into the wind so the drift will bring it back on target. The trace you are showing is a good day at our range, I've seen them with such a curve you wonder how the hell there they hit the target.

Joe Salt

 

[gunsandgunsmithing]

I don't know. The bullet experiencing the near wind (the first 500 yards) will follow a curved arc and and halfway down the range when the wind stops, it will be traveling in a different direction from when it left the barrel. I'm not going to attempt to calculate the amount of angular difference, but I think it's obvious that the flight path at the end of the first 500 yards is no longer parallel to the barrel. That being the case, it will continue to diverge from the POA during the second 500 yards even though the wind has stopped.

Me either. I will say this...If none of it is retained, the drift would be equal to the 500 yard drift of 11.19". If 100% of the drift is retained, would it not be double the 11.19..roughly, or 22.38"? Is that not saying that a 0 wind condition for the 2nd 500 has the same value as the wind for the 1st 500 yards did? How is that possible when the only basic outside forces acting upon it are forward and down. Again, I refer back to my analogy of dropping a marble from up high, letting it pass by a fan on the way down. I won't disagree that there may be a VERY short period when the bullets lateral momentum remains uncorrected, leaving the bullet flying non-parallel to the bore....but as long as we're guessing, I'm guessing that effect is very short lived before the bullet is again parallel to the bore but on it's new path to the target.

The best part of all is that there is no such thing as a no wind condition outside, so this is all just conversation.

Either way...hold into the wind and shoot well! Enjoy.--M

 

[fredo]

Joe,
That bullet actually started out with a down-slope 'tail wind' at about 7:00 from my shooting position. So, I was actually aiming with the close range wind. But yes, overall, the shot required a net right holdover to compensate for the greater L<--<--<--R wind across the valley. In effect, the minimal close range 'help' from the 7:00 wind allowed for 50% less hold on the far end. Which goes back to emphasizing the exponential effect close range wind has at distance...

Also, that big Norma wildcat launching a 215Hybrid at that speed is a friggin' laser beam & wicked wind-bucker. Not much 'rainbow' to that trace & makes the crosswind in the video look less significant than it would be to more conventional cartridges.

And, of course, familiarity with your range, whether it be square or field improvised, certainly helps with making a good call!

 

[Mozella]

...... snip........ Again, I refer back to my analogy of dropping a marble from up high, letting it pass by a fan on the way down. I won't disagree that there may be a VERY short period when the bullets lateral momentum remains uncorrected, leaving the bullet flying non-parallel to the bore....but as long as we're guessing, I'm guessing that effect is very short lived before the bullet is again parallel to the bore but on it's new path to the target.
..... snip.........

What exactly is the force, beginning at 500 yards at the point where the near wind quits, which you claim would return a bullet back to a path parallel to the bore once it is traveling on a nonparallel path? Look at it another way. Take any bullet path and ask yourself why it would suddenly change it's lateral path as if acted on by a wind, but without any wind present? In other words, if the near wind pushes the bullet into a curved path and then that force suddenly stops, wouldn't Newton's first law, which says in part ".........an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

In other words, at the 500 yard mark, the bullet is traveling at some lateral angle to the bore. What would make it then reverse this trend and turn to parallel the bore. Why, if there is no outside force, would it not continue at that angle, whatever it is, for the next 500 yards thereby taking the bullet further and further away from the POA?

Or, consider this slightly different situation. Set up a piece of steel at an angle of 45 degrees to your bore at some distance, say 500 yards. If you shoot toward this piece of steel the bullet flies nicely at first toward the target, again we're ignoring the effect of gravity and the much smaller effects of spin drift, and other minor factors. When the bullet hits the steel, it flies off laterally in some direction, let's say 45 degrees to the bore for argument's sake. That's similar to what a near cross wind does, but it happens all at once right at 500 yards where the steel plate is. Now once the bullet is flying on this new path, what force would tend to bring it back to fly parallel to the bore during the last 500 yards? None, the drift just prior to the steel is zero and the drift right after the steel is one yard laterally for every yard down range. Assuming there's enough energy remaining to travel 500 yards after the steel, the bullet would impact the target with a 500 yard lateral deviation, ignoring the fact that in the real world gravity would likely end the experiment early, but you get the idea.

In short, if the bullet is deflected from a path parallel to the bore onto a new path at some angle to the bore, when the deflecting force stops, the new direction will be maintained and the lateral error will continue to increase just like it does when you don't aim properly. If you fire when your rifle it is aimed to the right or left, the resulting error might be hardly measurable at 3 yards; in other words, even a pretty bad aim won't kill your chronograph. But down at the target that angular difference will be quite apparent and it will score worse and worse as the distance to the target is increased.

An additional thought experiment which you could actually conduct if you wished is this. Rather than drop something past a fan, set up a fan blowing across a ping-pong table. With the fan off, roll a marble from one end of the table to the other. It should roll in a nice straight line. Next with the wind blowing across just the first half, roll the marble again. It will follow a curved path downwind and when it rolls clear of the wind at the halfway point, it will NOT return to the original path. It will continue in a straight line (because there is no longer any lateral force) on the revised path which will be at some angle to the original direction. Depending on how long your table is, how strong the fan is, etc. that angular error will result in an increasing lateral difference between the POA and the POI, to use shooters terminology, as the marble continues along it's way.