Wind Induced Vertical

[Barossa_222]

Hi all. I was shooting on the weekend and we had a frontal fishtail and in the arvo it swung to a rear fishtail. This was causing vert shots on angle changes. Some guys got flogged around more than others. Are some bullet shapes more likely to be effected? VLDs vs Hyrbids etc

[Walt]

I suspect the phenomena, whilst observed, has never been scientifically tested. As such, any theories would be hypothetical at best. I suspect on blustery days, in a corridor type range, pressure vortexs can appear forcing a sudden and unexpected vertical shift. I doubt any amount of wind reading skills could see those. Therefore I feel the projectile configuration in those circumstances is a moot point.

[GSells]

Hi all. I was shooting on the weekend and we had a frontal fishtail and in the arvo it swung to a rear fishtail. This was causing vert shots on angle changes. Some guys got flogged around more than others. Are some bullet shapes more likely to be effected? VLDs vs Hyrbids etc

Variable Gyroscopic BC Torque and wind shear . It does exist !

[GSells]

Ok theory is simple and is this . In flight the bullet is in a slight nose up angle of attack and slightly to the right. Head wind makes the projectile have a slightly greater angle of attack . Creating more drag or lower BC and drop low . The reverse happens with a tail wind . Throw in a huge mountain of a back stop and large mounds and you get up and down drafts with the same drift as on the horizontal. Belmont is a great place to learn how to wind read in the vertical and horizontal. All though a few weeks ago it was nearly just unreadable. I feel light winds aren’t a problem till about 4-5 mph and it starts wind vectoring or fishtailing and this is where a wind reader earns their stripes . Try and shoot on the same vector . And if their is strong winds in your face or tail . Don’t shoot !!

[GSells]

Wiladia , did you want to add or correct me ?

[williada]

Done continuous experiments with left and right twists to further explore the phenomenon in the last few years to confirm experiments conducted from the machine rest circa 2002-3. The conditions you describe Barossa are the perfect storm but can be unpicked a little. Of course the results are worse in strong conditions over steep mounds and get worse with distance past the overturning point when velocity decreases sufficiently not allowing for the projectile to punch through conditions.

Two significant impacts occur, one from the compacted atmospheric pressure points over mounds or obstacles; and the other from the wind direction. Both influence the projectile's yaw of repose and vary surface area exposed to the direction of travel. Some bullets are more sensitive than others because they are longer and as a consequence the degree of yaw of repose of the bullet is increased with bullet length. So when comparing bullets, length is the better discriminator. Traditionally, VLD's have been longer than tangent ogive bullets. There are other performance values with hybrids which better relate to internal yaw as the bullet engages the rifling, so consider length first. VLD's perform best up to 12 mph with low drag over long distance IMO. Shorter tangents for the really rough stuff. Tight nodes on low velocity blow out in these conditions and is why I have a dim view of the imposed energy limits.

Generally speaking, when the projectile noses itself into the wind while travelling towards the target, it changes the drag characteristics when more surface area is exposed which ultimately reduces velocity along with subtle changes in angle of attack. The latter being greater or less depending on spin direction. In a fishtail,when the wind vector is changing from left to right or vice versa, there are changes to elevation spreads and you will probably notice in a RH twist barrel, left winds spreads are greater, but don't confuse this in mirage conditions and consider spin drift is a factor. This is not a problem to deal with in constant wind and direction such as the onshore Easterly in Sydney.

In a situation where the direction is constant, but the wind velocity surges, the projectile maybe subjected to significant aerodynamic jump. Hence in a right hand twist barrel the saying developed, "Left wind lowers, right wind raises". The degree of elevation spread depends on the barrel twist rate i.e. the faster the twist, the steeper the the lift or fall. A problem that may be associated with increased bullet length is the need to increase gyroscopic stability. An increase in twist rate may dampen the benefits of a higher BC projectile particularly when high winds are associated with high twist rates and aerodynamic jump needs consideration.

Frequent changes in atmospheric density occur e.g. where the pressure gradients are compressed over mounds and opened past mounds going in the eddies. This plays havoc with drag. Not the best place for a VLD.

When the wind angle changes from left and right or vice versa, it draws the nose towards the wind direction. The magnitude of change is greater when combined with frequent changes in atmospheric density. A further vertical effect depends on the direction of spin of the bullet and wind angle and this increases with distance as the bullet slows. The rate of spin does not decay much so the bullet nose raises and lowers a tad depending on spin direction in relation to the wind angle and the wind force.

If comparing calibres, then those with the greatest radial torque are more resistant to changes in yaw of repose. Hence a .223 gets bucked around more than a 30 cal.

In a standard atmosphere, the 7mm seems to be the most efficient slipping through the atmosphere. But if its too twitchy in some conditions depending on style or has reduced velocity due to energy limits, its benefits are dampened. So depending on condition strength, greater radial torque with a big 30 cal may be an improvement.

Generally speaking, the elevation effects between a frontal and a rear wind don't take much off velocity and group elevations and can be simulated on modern ballistic programs to reveal its relative insignificance. What is important is the atmospheric density and the different effect of forces applied to the nose by different wind angles along the range. But ask yourself if a surfing bullet on a hard rear wind is more problematic than a frontal in terms of nose orientation?

Sometimes the best strategy if elevation is a concern, is to determine where a condition lasts the longest and shoot that in a fishtail. In summary, changes in atmospheric density IMO are best counted by high velocity or projectile calibre with greater radial torque.

If all these conditions occured on the one day, it must have been a nightmare.

[GSells]

Sorry also answering the other question. Which projectile ??? My answer is a projectile that is high in bc and is properly dynamically stable at the range it is intended to be shot at .

180 vld’s and 180 hybrids in a 9 twist do this very well in my opinion and the accolades of the amount of Queens and international events seems to back that up .
Ok I had a go at 180 eld’s and they are a great projectile!! But in my experience up here in Qld with all of the wind shear and variable bc GT ( Gryoscopic torque ) . For me in a 9 twist barrel 180 eld’s are vulnerable beyond 800 yds . In my experience, win the conditions are stable at 1000 , they will shoot like stink and in the Belmont chop they go rather haywire as I saw in some of my et plots and others .
Somebody needs to try them ina 8.5 or 8.25 or even maybe an 8 twist and see how they shoot .
As for me , eld’s only at prize meets and club and not beyond 800 yds .
At 800 yds I’ve shot some great groups with the 280 ai slow loads at 800 yds . And testing and actually competing at 900 and then 1000 yds the groups opened up and sometimes erratically!

[GSells]

Done continuous experiments with left and right twists to further explore the phenomenon in the last few years to confirm experiments conducted from the machine rest circa 2002-3. The conditions you describe Barossa are the perfect storm but can be unpicked a little. Of course the results are worse in strong conditions over steep mounds and get worse with distance past the overturning point when velocity decreases sufficiently not allowing for the projectile to punch through conditions.

Two significant impacts occur, one from the compacted atmospheric pressure points over mounds or obstacles; and the other from the wind direction. Both influence the projectile's yaw of repose and vary surface area exposed to the direction of travel. Some bullets are more sensitive than others because they are longer and as a consequence the degree of yaw of repose of the bullet is increased with bullet length. So when comparing bullets, length is the better discriminator. Traditionally, VLD's have been longer than tangent ogive bullets. There are other performance values with hybrids which better relate to internal yaw as the bullet engages the rifling, so consider length first. VLD's perform best up to 12 mph with low drag over long distance IMO. Shorter tangents for the really rough stuff. Tight nodes on low velocity blow out in these conditions and is why I have a dim view of the imposed energy limits.

Generally speaking, when the projectile noses itself into the wind while travelling towards the target, it changes the drag characteristics when more surface area is exposed which ultimately reduces velocity along with subtle changes in angle of attack. The latter being greater or less depending on spin direction. In a fishtail,when the wind vector is changing from left to right or vice versa, there are changes to elevation spreads and you will probably notice in a RH twist barrel, left winds spreads are greater, but don't confuse this in mirage conditions and consider spin drift is a factor. This is not a problem to deal with in constant wind and direction such as the onshore Easterly in Sydney.

In a situation where the direction is constant, but the wind velocity surges, the projectile maybe subjected to significant aerodynamic jump. Hence in a right hand twist barrel the saying developed, "Left wind lowers, right wind raises". The degree of elevation spread depends on the barrel twist rate i.e. the faster the twist, the steeper the the lift or fall. A problem that may be associated with increased bullet length is the need to increase gyroscopic stability. An increase in twist rate may dampen the benefits of a higher BC projectile particularly when high winds are associated with high twist rates and aerodynamic jump needs consideration.

Frequent changes in atmospheric density occur e.g. where the pressure gradients are compressed over mounds and opened past mounds going in the eddies. This plays havoc with drag. Not the best place for a VLD.

When the wind angle changes from left and right or vice versa, it draws the nose towards the wind direction. This magnitude of change is greater when combined with in frequent changes in atmospheric density. A further vertical effect depends on the direction of spin of the bullet and wind angle and this increases with distance as the bullet slows. The rate of spin does not decay much so the bullet nose raises and lowers a tad depending on spin direction in relation to the wind angle and the wind force.

If comparing calibres, then those with the greatest radial torque are more resistant to changes in yaw of repose. Hence a .223 gets bucked around more than a 30 cal.

In a standard atmosphere, the 7mm seems to be the most efficient slipping through the atmosphere. But if its too twitchy in some conditions depending on style or has reduced velocity due to energy limits, its benefits are dampened. So depending on condition strength, greater radial torque with a big 30 cal may be an improvement.

Generally speaking, the elevation effects between a frontal and a rear wind don't take much off velocity and group elevations and can be simulated on modern ballistic programs to reveal its relative insignificance. What is important is the atmospheric density and the different effect of forces applied to the nose by different wind angles along the range. But ask yourself if a surfing bullet on a hard rear wind is more problematic than a frontal in terms of nose orientation?

Sometimes the best strategy if elevation is a concern, is to determine where a condition lasts the longest and shoot that in a fishtail. In summary, changes in atmospheric density IMO are best counted by high velocity or projectile calibre with greater radial torque.

If all these conditions occured on the one day, it must have been a nightmare.

Thank you David , you explain it better than I ever can !
But what he said

[bruce moulds]

just to muddy the waters further, there might well be some light bending between sight and target with different wind
possibly related to that, but not necessarily is the fact that for a wind from the right the bullet deflects a certain amount to the left.
however the allowance is more than that because the target image also moves to the left, a but like a boil makes the target image rise.
in the creedmoor days, from mind 1870s to 1912, shooters of black powder rifles used then had charts to predict vertical change with wind speed and direction changes.
if I can find my chart, I will post some examples. they were significant and needed to be dealt with.
the fact that there were charts would suggest either a hell of a lot of experimental firing, or that a mathematical equation could do the job.
match rifle shooters use some formula like 1 moa elevation for every 10 moa windage.
this has not proven the case with 284 win, and the 6.5/284 or 6.5 superlr.
bruce.

[williada]

Bruce you raise valuable information. Light does bend significantly with distance and atmospheric density. If there are different density layers present in the trajectory and the scope line of sight things can be very difficult. This is usually associated with light wind or nil wind. DaveMc made some terrific observations both at home and in the states with regard to mirage. Rarely does the boil raise the apparent aiming mark as it tends to be a mirror image down in hot climates, but in the states a reversal of this condition can happen in cold conditions. Please check the link, https://en.wikipedia.org/wiki/Mirage to distinguish between inferior mirage and superior mirage. Dave also gave permission to show his video of mirage over a cane field in Qld and the target movement as set up by Peter S. as posted on this site by ecomeat to demonstrate the boil pushed the aiming mark down.

That is not to say shots don't go high in boiling mirage in Australia but it more a function of lack of clarity in dense mirage and similar to the old army adage of "light up sight up, light down sight down". In the light down scenario, shooters tend to aim high when the light is dull. When it is bright and clearer they aim lower. In another condition of shadows, people are drawn to the bright side.

Subtle differences and adaption can mean points.

[bruce moulds]

from
the art of shooting with the rifle
by col. sir h. st.john halford bart, c.b
1888

figures for 800 yds.

20 mph wind from 2 o'clock
elevation adjustment 2 moa
from 1 o'clock
elevation adjustment 3.5 moa

these figures are comeups, and are greater than for modern rifles, and seem related to be related purely to drop caused by headwind.

left wind / right wind differences need more study.

going to 10 mph from 2 o'clock
elevation requirement is +1 moa
from 1 o'clock
about 1.75 moa.

these bullets had a b.c. of about or a bit more than 0.5 and a muzzle velocity of 1300 to 1400 fps, so were transonic for most of their flight, meaning more drag than for supersonic.
they were 0.450 to 0.460" diameter, so had good radial torque.

whether this is relevant to modern bullets at modern speeds who knows, but it does demonstrate elevation changes due to strength and direction.

muzzle velocity and time of flight are the 2 primary differences.
bruce.

[bruce moulds]

we must get different types of mirage.
I have never seen a target upside down.
and sometimes heat haze needs to be described as such, and not mirage.
bruce.

[williada]

Bruce, I will try and dig up the mirage video.

[williada]

Bruce I think this is it
viewtopic.php?p=66447#p66447

Click on the image in ecomeat's post. You have to wait a little for the image link to appear, on my old computer system anyway.

Added the direct link below to photobucket
http://i862.photobucket.com/albums/ab18 ... Namara.mp4

[Frank Green]

In a situation where the direction is constant, but the wind velocity surges, the projectile maybe subjected to significant aerodynamic jump. Hence in a right hand twist barrel the saying developed, "Left wind lowers, right wind raises". The degree of elevation spread depends on the barrel twist rate i.e. the faster the twist, the steeper the the lift or fall. A problem that may be associated with increased bullet length is the need to increase gyroscopic stability. An increase in twist rate may dampen the benefits of a higher BC projectile particularly when high winds are associated with high twist rates and aerodynamic jump needs consideration.

The attached sketch might help what Williada is saying about twist and wind direction.

I feel I exaggerated it some but that should give you an idea of what happens at times.

Williada, Very nice post!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Thanks for it!

Later, Frank