Wind Concerns - Long Range Shooting

FISMA

Just wondering which you consider to effect the bullet more, winds closer to the shooter or target for longer ranges, say 1000?

If the wind is closer to the shooter, the bullet is going fastest. Thus, the time in the wind is minimized. However, the remaining flight time, or distance is maximized. A lot like how a MOA changes over greater distance.

Likewise, wind closer to the target effects a slower bullet. Thus, the time over which the wind's force acts on the bullet is greater. But there is not as much distance as before for deviation.

I understand that there are umpteen more variables to deal with and even more constraints for the given circumstance. However, I am just wondering what the long range shooters worry more about: all things considered equal, a wind near the shooter or target?

bravestar

FISMA wrote: »

Just wondering which you consider to effect the bullet more, winds closer to the shooter or target for longer ranges, say 1000?

If the wind is closer to the shooter, the bullet is going fastest. Thus, the time in the wind is minimized. However, the remaining flight time, or distance is maximized. A lot like how a MOA changes over greater distance.

Likewise, wind closer to the target effects a slower bullet. Thus, the time over which the wind's force acts on the bullet is greater. But there is not as much distance as before for deviation.

I understand that there are umpteen more variables to deal with and even more constraints for the given circumstance. However, I am just wondering what the long range shooters worry more about: all things considered equal, a wind near the shooter or target?

Generally speaking Near wind causes the geatest deflection in relation to POI and far wind modifies the value of the near wind, + or -.

DMW22

I was always concerned more with near wind as bravestar said it has more of an effect on poi but of course all wind is equally important.

clivej

Easy answer is the smallest amount of movement nearest the shooter will have a greater effect down-range. So with a strong wind nearest the shooter it will push the round more than having a strong wind nearer the target.

Ziggieire

clivej wrote: »

Easy answer is the smallest amount of movement nearest the shooter will have a greater effect down-range. So with a strong wind nearest the shooter it will push the round more than having a strong wind nearer the target.

I am not saying you are incorrect but that does not make sense to me.

if we take velocity change and friction out of the equation for a minute,
and the cross wind is at an equal speed all the way to the target at 1000m.
Once the bullet leaves the gun it is not anchored at any point, no matter where along the flight path you push the bullet to the side with a 20 kph gust it will always drift the same amount.

If we put velocity back in lets say 3280fps, with noraml bc and friction it will hit the target in what about 2 seconds ?im not sure.
But it will have its greatest speed and twist in around the first 1/3 or 1/4 of the flight surely it would have the highest chance to resist the wind pushing it in the first .5 of a second of flight ?

That how it is when i think of flight, so im not sure how the wind could effect it more in early flight than later

ejg

Wind changes the direction (or angle) of flight. If the direction of flight is changed right after leaving the barrel the offset at the target is larger than if wind is close to the target. Or, a small wind at the barrel can have a much bigger affect on the overall drift than a strong wind close to the target.

Draw a straight (zero) line on a piece of paper, mark a spot where the shoot is and where the target is on that line.
Draw a line a few degrees off the zero line going through shooter position (wind at muzzle area), then draw a parallel line to that going through the zero line half way to the target (wind at halfway). You will see the line with wind at the muzzle is more off target than the one half way down.
Wind in the same direction all the way to the target will lead to the bullet flying on a curve as the angle is increasing as the bullet flies to the target.
Consistent wind makes the flight path look like a ballistic curve just lying on it's side.
edi

Ziggieire

ejg wrote: »

Wind changes the direction (or angle) of flight. If the direction of flight is changed right after leaving the barrel the offset at the target is larger than if wind is close to the target. Or, a small wind at the barrel can have a much bigger affect on the overall drift than a strong wind close to the target.

Draw a straight (zero) line on a piece of paper, mark a spot where the shoot is and where the target is on that line.
Draw a line a few degrees off the zero line going through shooter position (wind at muzzle area), then draw a parallel line to that going through the zero line half way to the target (wind at halfway). You will see the line with wind at the muzzle is more off target than the one half way down.
Wind in the same direction all the way to the target will lead to the bullet flying on a curve as the angle is increasing as the bullet flies to the target.
Consistent wind makes the flight path look like a ballistic curve just lying on it's side.
edi

I don't think that a normal wind could change the angle of the bullet in flight, the gyroscopic effect the rifling imparts on the bullet would make that very hard to do.
it will push the bullet with the wind but I would not think the angle would change, if it did then on big wind calls you would see a slight keyhole on the paper.

I have no doubt that the curve would look like a smaller version of a bullet drop but if anything it would have a sharper curve near the end of a long flight path, not at the beginning.
when it has lost some spin and energy.

ejg

What do you think then?
the bullet gets pushed to the side via wind and then turns in s-form back on the same angle it previously had...magic!

edi

Ziggieire

ejg wrote: »

What do you think then?
the bullet gets pushed to the side via wind and then turns in s-form back on the same angle it previously had...magic!

edi

No you offset your shot and have it pushed back on target.
But the bullet it self cannot be Tilted by the wind, it can be shifted but its angle stays the same. if the wind could change the pitch of the bullet you would have a whole new problem.

What i have a hard time beliving is

Easy answer is the smallest amount of movement nearest the shooter will have a greater effect down-range

Yes the smallest amount of movement when it has a pivot point while still in the chamber will cause big error down range.
But i don't believe wind impacts the bullet more early in the flight path than later. As it will not change the angle of the bullet only push it along.

It only makes sense that wind would effect a bullets flight more as it slows down, Not at the muzzle or 20 meters out where it has the most enegery and spin to fight outside factors once it has left the barrel.

patsat

Ziggieire wrote: »

No you offset your shot and have it pushed back on target.
But the bullet it self cannot be Tilted by the wind, it can be shifted but its angle stays the same. if the wind could change the pitch of the bullet you would have a whole new problem.

The bullet doesn't have to change angle for it keep moving laterally because of the wind. Pretty much an example of Newtons Law. An object in motion wants to stay in motion.

So if the wind cause the bullet to move in a certain direction, it will stay moving in that direction.

Ziggieire

patsat wrote: »

The bullet doesn't have to change angle for it keep moving laterally because of the wind. Pretty much an example of Newtons Law. An object in motion wants to stay in motion.

So if the wind cause the bullet to move in a certain direction, it will stay moving in that direction.

Yep you are correct it wont travel for ever. spin drift can offset it and are resistance will also slow the lateral movement.

But that is not what i asked.
I am questing the statement that less disturbance will cause more movement .
i know what peopel are saying one millimeter at muzzle is a few inches down range. and that is true

But you would need a lot force to move a bullet that just came out of a muzzle doing 3000 fps.
Than it would to move a bullet thats doping transonic at 900 meters.

ejg

Once a bullet has changed it's direction it will only change direction again due to outside forces.
if the wind changed the direction of say 1 deg and stops blowing then the bullet keeps the 1 deg angle.
You'd need wind from the other side to get it back to 0 deg.

Drive a high speed motorbike on an open road, side wind will change your direction, until you steer back on track.
edi

FISMA

Rotational accelerations, pitch, and yaw are a whole other kettle of fish. I am trying to keep it simple, just to try and start to wrap my head around things.

Let's say there is no wind and you are hitting the bullseye.

Now there is a left to right crosswind for the first 100ya and an equal crosswind, in the opposite direction for the last 100ya.

Do you expect to hit the bullseye dead on, left of target, or right?

I would think right of center.

Before the shot, pretend there was somehow a laser light shining through the center of the barrel right to the bullseye. This will be our reference line.

Next, we shoot and the bullet leaves the barrel.

For the first 100ya, the bullet is pushed to the right. If the wind is constant, an overhead view of the bullet would be parabolic and not a straight line.

For the first 100ya there is a side wind Force. Looking down from overhead (2-D, forget the drop due to gravity) we see the bullet travel towards the right in a parabolic arc, not a straight line. Thus, we are not on the reference line of the laser.

At the end of the 100ya there is no longer a side wind so the bullet (as viewed from above, forget the drop due to gravity) travels in a straight line. However, this line is not inline nor parallel to the laser. The path of our bullet is straight, but at an angle to the laser line.

For the next 800ya, the bullet continues on its way and has 800ya over which to deflect.

Now comes the 900ya line and the opposite crosswind. The bullet, going slower, now has more time to be affected by the wind, but less distance to target.

The bullet no longer travels in a straight line since it is being pushed to the left by a constant force. With respect to the straight line in which it was traveling, I believe the bullet will deviate, back left, in some kind of curve.

The problem with figuring all this out is that one of our variables may mean more than the other with respect to deviation. That is, it could be a term that is squared.

For example, we know that the Kinetic Energy of our bullet, KE = ½mv² where m is mass and v is speed.

From the equation, we see that speed matters more than mass since it is squared. If you double the mass of the bullet, you double the KE. However, if you double the speed of the bullet, you quadruple the KE.

I bet something like this will come in to our analysis. Speed may even be cubed.

I think I need to figure out how much time the bullet spends in the 100ya, 200ya-900ya, and from 900-1000ya. I think this would help.

Any Aerospace Engineers out there?:rolleyes:

Thanks for the replies, keep em coming.

clivej

Fisma you have answered your own question really.

If in the 1st 100y the wind has pushed the bullet off the bullet will keep going in that direction for the next 900y (100 with wind + 800 no wind). And keep going off at the same angle away off your laser line of sight. Now work out the time it took to get to 900y and the velocity at 900y.

Now you need to get back to the the POI but the bullet is still travelling quite fast but you only have 100y to do this.



Zero = 1000y, velocity = 2800 fps, 30 cal 155gr bullet

Using Strelok+ ballistics program on my phone it will push the 30 cal bullet...
.7 inches at 100y inches in a 10mph cross wind, and will keep going off at that new angle which is .7MOA
Time to 900y = 1.41 seconds
Energy = 618.8 ft-lb

Time to 1000y = 1.64 seconds
Energy = 511 ft-lb

The round has been going cross wind for 1.41 seconds.
So in that last 100y you have .23 seconds to move the round back to the POI.
The thing to remember is once the round had started to drift it continues on in the same direction. It doesn't return to the parallel of the laser line but keeps on that .7 MOA drift.


Here is the experts view on the theory
http://www.longrangehunting.com/articles/shooting-crosswinds-1.php

ejg

Sounds right Clive,
the down range opposite wind must first get the 0.7MOA drift back to zero (parallel to the laser line) then only will it start to direct the bullet back towards the aimed target.
So if you had left to right cross wind in the first 100yds it will dominate and your shot will be well to the right off the laser line even if you had the last 100yd right to left wind.
edi