Vertical dispersion at 600 yds to 1000 yds

[DaveMc]

It is amazing how a really accurate rifle "calms" a lot of this "vertical" .

What Bryan Litz and others are saying is the effect of a head wind or tail wind is minimal with regards to the scale of a 10mph headwind in relation to a projectile doing 3000 odd fps.
10mph is around 15 fps - you can look at the table we put on the es/sd thread to get an idea of effect. Head winds and tailwinds WILL NOT change the pitch and yaw anymore than similar change in bullet velocity. It is all due to "relative velocity" in the air. So in regards to the expected bullet drop due to pure wind vector is is unlikely to be significant except in extreme pickups and drop offs.
Put this in perspective - we need to be reading wind to around +/-0.5 - 0.7 mph to stay in the 6 ring at 1000 yards What sort of effect would a headwind have if read to same level - not much!!

HOWEVER - there are other factors to consider.
1) Aerodynamic Jump - the 10:00 to 4:00 slope. This varies with gyroscopic stability but in general can be enough to make half a minute of vertical from just a couple minutes left to a couple right. Much more if severe fishtail. This is where high BC helps. The slope of the line is a factor of gyroscopical stability but the more wind you have on the same slope will result in bigger movements. ie a 308 moving 6M left to 6M right will heva more elevation change than a 7mm doing 4L to 4R
2) The change in mirage and temperature fields as the air flows over mounds and other geographical disturbances
3) There are other factors proposed such as vertical wind vectors (sheer) and pressure changes over mounds etc. I am sure they exist but once again the scale of these is probably minimal in most bar extreme cases.

In reality a combination of the above and more could have some noticable effect.

BUT - One of the biggest issues we face is "perceived" issues and range talk. As soon as we get a bad group or plot on a windy day then it is all due to the wind. even more so if several people find same. If it happens on a calm day then we might tend to think of it more as a rifle accuracy issue. As I said it is amazing how much of this vertical goes away with a hummer.

The other issue is misreading groups. - See the next thread I am about to start on sampling and groups. It is very easy to interpret the wrong story from 1 or 2 shoots - especially when there is a bit of variation in the vertical to start with.

[plumbs7]

Thanks everyone for your contributions! As always very informative! Regards Graham!

Hmm , must try that with the Yak, maybe just before the Queens and test the wind for everyone!

[Norm]

Thanks everyone for your contributions! As always very informative! Regards Graham!

Hmm , must try that with the Yak, maybe just before the Queens and test the wind for everyone!

An interesting experiment would be to get a few out of date boat flares and set them off on a day when there is no shooting taking place. Ideally on a day where the wind is running up or down the range.
The smoke will give you an idea of just what effect the terrain has on the wind.

[AlanF]

...An interesting experiment would be to get a few out of date boat flares...

We may be able to get help with this from another sport - some Melbourne soccer hoons are looking for a place to set off their flares without getting life bans .

[RDavies]

Thanks everyone for your contributions! As always very informative! Regards Graham!

Hmm , must try that with the Yak, maybe just before the Queens and test the wind for everyone!

An interesting experiment would be to get a few out of date boat flares and set them off on a day when there is no shooting taking place. Ideally on a day where the wind is running up or down the range.
The smoke will give you an idea of just what effect the terrain has on the wind.

The best example of this I have seen is a few years ago at a Queens at Malaba, I was discussing with some newer shooters how, when the wind was from the left and you are shooting over the RH edge of the gully on the left 3rd of the range that your shots will hit higher than your normal zero. Just as I was talking about it, some kids balloons blew over the range from the beach. As they blew along the gully, they were flying along level with the ground. As they got to about 20 foot before the end of the gully, they blew straight up about 15-20 foot, then continued along on level flight again.
Another example I saw of this was at my last prize shoot at Hornsby range I was watching through my spotting scope and noticed that when the wind was from the right, the puff balls (or whatever those hairy seeds you see blowing along the breeze are called) blew over the big wall on the right side of the range, then about 15-20 feet past the wall, they would drop straight down a few feet before flying along level again. I have seen them do similar things on the far left of the range at Belmont at long range as they went over the mounds. These winds don't seems to have a major effect on 7mm bullets as I haven't lost any shots in vertical at these ranges in a long time which I couldn't put down to other recognised factors, and certainly no where near the 4 ring.
There are numerous other ranges where locals know that certain sections of the range will give you more vertical than other sections in certain wind conditions ie, if you are on the far left of Canberra range and wind is quartering from the left, you will get more vertical from the mounds. If you are on the far left of Wagga Wagga SSAA range you will get vertical at 500M no matter where the wind if from due to the big steep walls and gullies on the left side. From what I have experienced, these effects would cause a 7mm bullet to use more of the 6 ring in normal conditions, but not give wild 4s or anything under regular conditions.

[KHGS]

Thanks everyone for your contributions! As always very informative! Regards Graham!

Hmm , must try that with the Yak, maybe just before the Queens and test the wind for everyone!

An interesting experiment would be to get a few out of date boat flares and set them off on a day when there is no shooting taking place. Ideally on a day where the wind is running up or down the range.
The smoke will give you an idea of just what effect the terrain has on the wind.

The best example of this I have seen is a few years ago at a Queens at Malaba, I was discussing with some newer shooters how, when the wind was from the left and you are shooting over the RH edge of the gully on the left 3rd of the range that your shots will hit higher than your normal zero. Just as I was talking about it, some kids balloons blew over the range from the beach. As they blew along the gully, they were flying along level with the ground. As they got to about 20 foot before the end of the gully, they blew straight up about 15-20 foot, then continued along on level flight again.
Another example I saw of this was at my last prize shoot at Hornsby range I was watching through my spotting scope and noticed that when the wind was from the right, the puff balls (or whatever those hairy seeds you see blowing along the breeze are called) blew over the big wall on the right side of the range, then about 15-20 feet past the wall, they would drop straight down a few feet before flying along level again. I have seen them do similar things on the far left of the range at Belmont at long range as they went over the mounds. These winds don't seems to have a major effect on 7mm bullets as I haven't lost any shots in vertical at these ranges in a long time which I couldn't put down to other recognised factors, and certainly no where near the 4 ring.
There are numerous other ranges where locals know that certain sections of the range will give you more vertical than other sections in certain wind conditions ie, if you are on the far left of Canberra range and wind is quartering from the left, you will get more vertical from the mounds. If you are on the far left of Wagga Wagga SSAA range you will get vertical at 500M no matter where the wind if from due to the big steep walls and gullies on the left side. From what I have experienced, these effects would cause a 7mm bullet to use more of the 6 ring in normal conditions, but not give wild 4s or anything under regular conditions.

Yep, one of the things I have been alluding to all along, unseen/unidentifiable air currents that the bullet must pass thru on it's way to the X waaay down range. We need tight symmetrical groups with low extreme (sd) spreads for sure that goes without saying, but all that will not prevent vertical caused by unidentifiable air currents. Some bullet designs seem to handle this problem better than others. Having said that though it is very hard to quantify this problem, no mathematical or scientific table or graph can help, difficult to graph something that can't be seen or measured.
Keith H.

[johnk]

Belmont Small bore range has a cute issue some winter nights when you get a meniscus or the like between the cool night air & hot ground air that forms exactly on the line of the aiming marks, causing high & low eights was it washes like ocean waves.

[plumbs7]

Belmont Small bore range has a cute issue some winter nights when you get a meniscus or the like between the cool night air & hot ground air that forms exactly on the line of the aiming marks, causing high & low eights was it washes like ocean waves.

Well that is the next thing is mirage !

This load showed 1-2 feet ps spread with a spike last shot! The mirage was heavy and boiling left !
Was pretty much the same load as the test target as the one I posted before! It's all over the place !
The bottom group was 168's in good sighting conditions and a annoying high shot again in the middle!

Another group pretty much the same load again but right on dusk with boiling mirage and slight left wind!
Norm I think a smoke experiment would be interesting!

[williada]

You’re killing me Plumbs. The apparent aiming mark shifts down not up in many cases. Depends on whether you are a fish or an eagle. Where is the refraction happening? I’m probably a fish. David.

[plumbs7]

You’re killing me Plumbs. The apparent aiming mark shifts down not up in many cases. Depends on whether you are a fish or an eagle. Where is the refraction happening? I’m probably a fish. David.

This is appropriate in today's political environment! " Please explain!!??"

Umm up here on the western downs it seems to go the opposite way!
That one with 3 groups was shot just before the sun went down! I must need glasses as I obviously saw 3 different aiming marks ! Oh hang on I was wearing glasses ! Haha!

[williada]

Hey Graham, you’re killing me because you are asking great questions. I am laughing with you. If DaveMc can post a mirage video, you will be laughing too. It’s not my place to post it. It will certainly make you think if you are a fish or an eagle because your view through the mirage is completely different with regard to apparent shifts depending where you sit. I just don’t want to explain because as you know it becomes too wordy. That is killing me. I cannot upload the video because my internet is shaped at present. That is killing me too.

[williada]

Hey Tony,
Dave might give you permission to post it. If you have a copy. David.

[ecomeat]

Hey Tony,
Dave might give you permission to post it. If you have a copy. David.

Hopefully he will chime in here . I have a copy but would need to load it onto Photobucket.com to be able to have a useable link

[DaveMc]

Ok,
i will make a quick input here thanks guys,
Tony - You cvan post it if you wish. unfortunately I lost a LOT of stuff on a computer crash (Also took out my backup) with a lot of video of this and more.

Plumbs what David is referring to is Inferior and Superior mirage (google it to save me writing too much). What we mainly see as shooters though (lying on the ground with hot ground) is an apparent image shift down due to refraction as the heat gradient increases. e.g. sun comes out from behind a cloud and mirage starts to come on. Through the scope it looks like it is "rising" due to the scintillation waves but in reality refraction is bending the image down. The video these guys are talking about is a short time lapse of one of the ones I took at the farm during a particular 45 minute period where the clouds came over a few times.

Peter Smith and I spent a great deal of time a few years ago (with help of a few others up here) trying to map this and also plot fall of shot with relation to image movement. Peter built some specialist scopes with adjustable crosshairs and video attachments.

We captured image shift of up to 1.0 - 1.5 minutes in extreme conditions over a cane paddock (very humid air rising out of the mulch). But interestingly enough it was very hard to map a similar POI change in a shoot. When conditions were bad, accuracy fell off and although there would be small rises and falls there seemed to be a "counter" movement of similar magnitude to the mirage in the places we were testing. We are still hypothesizing about those but never got to finish the work - and as said in one of the previous posts - "how do you measure" some of these factors.

Things got real messy when the wind was quartering through heavy mirage and over banks etc. The image just went nuts.

The general take home message of this - although thee is a significant image shift due to mirage effects. There are other things at play. If you read the mirage article from Texas you will get totally confused as they "wind" the opposite way to the mirage (refraction) movement. Either the corresponding "other factors" are larger in magnitude or they had some serious typos. Either way I would not put anything they wrote into practice anywhere we have shot. (We are upside down down here of course)

For you Graham - On my farm the air stabilised amazingly after about 4pm and even with crazy winds I could do fantastic testing every afternoon. The mornings had serious issues. I had bad mirage in the mornings (cold ground warm air and even the reverse the odd cold katabatic breeze (cold air coming down off the mountains) over warm land. Late afternoons the air temps started to match ground temperatures and refractive gradient would dissapear - so would a lot of "vertical" issues with the rifles.

Dave

[jasmay]

So, the important question is how to manage it effectively?

Explaining the why and how is great, but what is of more use to shooters is how we manage it.