Headwind causes bullets to hit high @ 600?

[mattri]

Interesting experience at the range.

Am shooting a 7mm-08 using 150gr SGKs. Have been shooting this rifle/load for about a year, it is my go to combo. Have shot this load over a chronograph on numerous occasions under various conditions and shoot out to 600 regularly. Using a Viper PST with the EBR-1 reticle, holdovers are well known and consistent.

On any given day can shoot at 100-600 yards and know exactly where to hold to hit the gongs. Not a BR set up by any means but sub-moa more often than not.

The range I shoot at is on a hill at the end of a good sized lake so the wind is always tricky but the other day it was coming straight up range, a 12 o'clock value at about 15mph.

Figured I needed to hold a little high so held 1 mil high @ 600 and shot over the gong. Shot again to confirm, same poi. Held 1/2 mil and same result, over the gong. Held on the regular hash for 600 and just over the gong.

Ended up holding a full mil LESS than normal and rang the gong time after time.

How does a 15mph headwind cause a bullet to hit high @ 600?

 

[Keith Glasscock]

Orthographic lifting... A fancy term for air hitting a piece of terrain and being directed upward. It could be that and/or the range is uphill making the oncoming wind strike more of the bottom of the bullet.

With all of that in mind, was it warmer out than previous outings? How was the humidity compared to normal?

 

[mattri]

Temp and humidity were consistent with previous sessions. The shooting line is at approximately the same elevation as the 600 yard line, with a valley between the two.

 

[Immike]

Mr Busdriver made a good point and I have experienced the air flow following the slope of the field from the left and right as well. Some ranges have several shorter backstops that are shot over that create elevation problems with a head wind, I shoot on one!!

 

[drover]

The effect of each of the three components of any wind is quite different. This is because the aerodynamic drag on a bullet is a function of the bullet’s speed with respect to the air through which it flies. Therefore, if the air is moving, the drag on the bullet is different than it would be if the air were still. For example, 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. Generally, unless the wind speed is high and the range is very long, a headwind or tailwind causes only a small deflection of the bullet relative to the still air trajectory.

The whole article - http://www.exteriorballistics.com/ebexplained/5th/32.cfm

drover

 

[pacificman]

Good responses...I think of headwind or even tailwind in more simple terms. I think of it as wind-shear. I used to pilot rc aircraft in pylon races and watched as the plane flew into the wind. A strong wind could cause the plane to dive or lift with very little input on the controls. I know that a bullet and wing are two different things but it all seems to act the same. Go ahead and laugh but I guess for me you could say "simple things for simple minds" : ;D

 

[Cakes]

"with a valley between the two".... Very common phenomenon with regards to wind-terrain & effect. Eric in DL

 

[Hombre0321]

The effects of a Head Wind and Tail Wind are very well known in the shooting world. In your case there must have been something else going on for you to have had the results you did.

A headwinds effect on the bullet is to drive it down not up, just the opposite with a tailwind. So for you to have had a completely different result than is "Standard" means something else must to have been going on. Here is a simple chart that has been in use for decades and I have never seen it wrong, if I was reading the conditions correctly or there was something else happening that you did not detect.

 

[people]

I like that chart.

I have two 308 rifles that shoot almost the same ammo. To get the same speed one gets just a smidge less powder than the other. Any way one shoots high into the wind and the other shoots low into the wind.

 

[stool]

is one rifle right hand twist and the other a left hand twist ???
the chart is right hand...everything changes with a left hand twist

I like that chart.

I have two 308 rifles that shoot almost the same ammo. To get the same speed one gets just a smidge less powder than the other. Any way one shoots high into the wind and the other shoots low into the wind.

 

[John from MN]

"with a valley between the two".... Very common phenomenon with regards to wind-terrain & effect. Eric in DL

See above.

I'm always a little frustrated when I go after pdogs because my drop charts are nearly useless in the broken country where we shoot them.

 

[M14AMU]

It could be that you were holding roughly 21" above your standard hold using 1 Mil @ 600 yds.

 

[gunsandgunsmithing]

The effects of a Head Wind and Tail Wind are very well known in the shooting world. In your case there must have been something else going on for you to have had the results you did.

A headwinds effect on the bullet is to drive it down not up, just the opposite with a tailwind. So for you to have had a completely different result than is "Standard" means something else must to have been going on. Here is a simple chart that has been in use for decades and I have never seen it wrong, if I was reading the conditions correctly or there was something else happening that you did not detect.

Listen to Roland, here. He knows what he's talking about..and I happen to agree. The only man to defy physics walked on water.

 

[mattri]

Interesting replies thanks.

The wind was definitely coming from 12 o'clock.

As to the need to hold an entire mil high that certainly could have been too much, but does not explain needing to hold a mil less than normal.

The valley is slight, but very well may have been the culprit, will have to watch for similar conditions and try to repeat the experiment. Always more to learn, especially about wind! Thanks again for all the great info.

 

[LHSmith]

Field Mirage (as opposed to bbl. mirage)- you were aiming where the gong appeared to be, not where it actually was. You hit on a condition that day that was not present on previous outings. This is the whole reason behind sighters. Charts are a good generic guideline, but sighters tell the real the story in real time.....you just have to be quick enough to hit "THAT" condition.

 

[mattri]

Interesting idea- thanks again!

 

[maxpower]

Drover, I read your article on cross winds, head winds and vertical winds and was hoping you can clarify something.
The 284 shooting 180gn bullets has similar wind drift to a 308 shooting 230s. Does this mean at a range like mine with various mounds, logging road and gullies, a 308 shooting the heavier bullets will still have the same amount of range induced vertical as the 284? One of our F TR guys has been telling us his 308 is less affected by the range head/tail wind induced verticals than our F Open 284s.

I know at our range, when the wind is from front or back, we all seems to get the verticals, but local folk law says the heavier bullets are less affected due to their more momentum, is this false reasoning?

 

[dannyjbiggs]

Interesting replies thanks.

The wind was definitely coming from 12 o'clock.

As to the need to hold an entire mil high that certainly could have been too much, but does not explain needing to hold a mil less than normal.

The valley is slight, but very well may have been the culprit, will have to watch for similar conditions and try to repeat the experiment. Always more to learn, especially about wind! Thanks again for all the great info.

And take a note from Hombre's wind vector chart! It shows that headwinds out of 11 and 12:00 o'clock stream low, while from 1:00 o'clock (still a headwind) stream to above center, a little high. Shooters frequently get caught on elevation shots in the 11 to 1:00 o'clock headwind area! For example, say the wind was coming at you fairly steady at 12 (or 11), you initially fine-tuned your elevation zero upward in that condition because POI was low, and a little later the wind eased over to 1:00 and you did not note the change, still feeling a headwind in your face....there comes your elevation shot. The converse is true for the tailwind at the 5 to 7:00 o'clock area. Of course, wind intensity is clearly the main factor. Most of the time, F-Class shooters will just see highs and lows in the X-ring, but buck up the wind velocity, and things can get nasty if one is not observant to wind direction change relative to the condition that elevation was initially fine-tuned.

A couple of years ago during one of the 1000 yard matches at the Raton F-Class Nationals, shooters were confounded by (unexplained) high 9's and 8's in a blistering wind flag cracking headwind?? When we laid down to commence that match the wind flags were stampeding out of 11:00 o'clock, flickered over to 12 and back a couple of times and then flickered over to 1:00...you could plainly hear the groans up and down the line, and this was repeated...shooters got caught more than once!! (It's not just the firing line berms to your front at Raton!)

Danny Biggs

 

[drover]

Drover, I read your article on cross winds, head winds and vertical winds and was hoping you can clarify something.
The 284 shooting 180gn bullets has similar wind drift to a 308 shooting 230s. Does this mean at a range like mine with various mounds, logging road and gullies, a 308 shooting the heavier bullets will still have the same amount of range induced vertical as the 284? One of our F TR guys has been telling us his 308 is less affected by the range head/tail wind induced verticals than our F Open 284s.

I know at our range, when the wind is from front or back, we all seems to get the verticals, but local folk law says the heavier bullets are less affected due to their more momentum, is this false reasoning?

Yes/No/Maybe.

Thanks for asking my opinion on this but it is not a discussion I really wish to enter into because they generally end up being spitting contests. In the end folks still believe what they want and it is difficult to prove definitively otherwise. There are many factors to consider such as the ballistic co-efficient of the various bullets being used, speed of the bullet (fps), humidity, elevation, etc. I recommend that they take a look at http://www.jbmballistics.com/ and program different scenarios there. But in the end they will still end up believing what they want. Exterior ballistics may be mathematically predictable but in the end there is still a lot of black magic and voodoo that is unpredictable.

drover

 

[savagedasher]

Drover, I read your article on cross winds, head winds and vertical winds and was hoping you can clarify something.
The 284 shooting 180gn bullets has similar wind drift to a 308 shooting 230s. Does this mean at a range like mine with various mounds, logging road and gullies, a 308 shooting the heavier bullets will still have the same amount of range induced vertical as the 284? One of our F TR guys has been telling us his 308 is less affected by the range head/tail wind induced verticals than our F Open 284s.

I know at our range, when the wind is from front or back, we all seems to get the verticals, but local folk law says the heavier bullets are less affected due to their more momentum, is this false reasoning?

Yes/No/Maybe.

Thanks for asking my opinion on this but it is not a discussion I really wish to enter into because they generally end up being spitting contests. In the end folks still believe what they want and it is difficult to prove definitively otherwise. There are many factors to consider such as the ballistic co-efficient of the various bullets being used, speed of the bullet (fps), humidity, elevation, etc. I recommend that they take a look at http://www.jbmballistics.com/ and program different scenarios there. But in the end they will still end up believing what they want. Exterior ballistics may be mathematically predictable but in the end there is still a lot of black magic and voodoo that is unpredictable.

drover

+ more then one time on the voodoo Man