cross winds & downdrafts at 1150 & 1625

[BigBboy25]

The pressure shift in the Kestrel I find interesting because it is the same air, so to speak, it is justing swirling off the ridge, I understand if your losing or gaining elevation, but if your ele. stays the same your pressure shouldn't fluctuate with moving air (unless a front is coming or going). Maybe someone else can chime in here and share

Well, according to fluid mechanics, when fluid velocity increases, pressure decreases. (Bernoulli's equation shows this very clearly.) This is what allows air planes to fly (at a very basic level!). The wings are designed so that the air is moving faster on top of the wing than on the bottom. this causes there to be lower pressure on top of the wing and higher pressure below the wing, thus generating lift. Keep in mind that the top of the wing and bottom of the wing are roughly at the same elevation but the pressures are very different on each side of the wing. . . just something to think about.

As to the pressure changes experienced on the Kestral, my guess is the 'burbles' are lower pressure areas. So if you're on the right spot on the mountain where one of those is occurring, you may see a small pressure change on the kestrel. However, it is nearly impossible to say how big that 'burble" area is, so I do not know if you would need to account for it for a 1500-2000 yard shot. If you only shoot through 200 yards of the 'burble' area, then the remaining 1,300 yards are in relatively static air, I'm not sure you'd need to account for the pressure change in the 'burble'.

This is just my hypothesis however. Using what I know of fluid mechanics and trying to piece things together. I think the best thing to do would go out there and sling some lead and see what happens. Very interesting stuff!

 

[BrentM]

So one of the things I think about, shooting from one ridge to another for example, is what is all that air is doing in the middle. It seems like a great deal of the shots people take are down a ridge, finger, or across ground. The winds do all sorts of things in those areas. However, I have been looking at the bullet flight path more and more vs what I see happening on or near the ground.

For example a few weeks ago I shot at 1200 down into a valley. The wind was traveling right to left and from behind me. I could not tell what is was doing at the target until I saw the impact dust blow L to R. I adjusted and sent it, hit, 1 more adjustment sent it, bingo. Ok, at the time was concerning myself with felt wind at ground level vs the bullet traveling 300 ft above the surface. I am pretty at the bullet elevation wind was Prevailing and had no ground affect at all.

Wish ammo and powder were easier to come by so learning had less cost associated with it.

 

[X-man]

Some interesting thoughts here.

The terrain I shoot in is steep yet has small peaks and valleys. I often shoot from one mtn top, over a short valley, across a shorter/lower mtn top and then across another short valley, to the up slope of another small mountain all to get 1500 yards!....The corrections are nightmarish.

I am a little haywire, but let me share how I do it.
Your opinions would be greatly appreciated.

I find the only way I am able to deal with the problem is to draw a map and mark out wind direction and thermals then break the bullet flight into shorter segments (the sections I am unsure of I try to shorten). I have run the calculations exactly like that with decent results, but re-calculation (without a smart spotter) is slow and near impossible to make corrections for once you have a change. To top it off there always seems to be a significant elevation change that needs to be worked into the mix

In other words on a 1500 yard shot I break out the first 400 yards down slope (I can estimate these winds pretty easily), then I estimate the cross valley shot starting a the end velocity/yard mark of the 400 yard shot, then up the other slope and so on until I connect all of the segments.
Mirage is my only friend.

Anyone else do it like this or am I nuts?

 

[CA48]

And I get fluttered when I have to deal with more than
one crosswind going in the opposite direction.

Very interesting discussion to us flat landers. As Texas
has very little topography change.

 

[larks99]

Crosswinds don't just move a bullet left or right, but actually move a bullet up and down depending on the direction. Crosswind moving left to right will move the bullet down. Winds moving right to left will cause the bullet to rise. I believe this explains why you had to make an elevation adjustment.

 

[Danehunter]

Yeah, wind, the eternal long range shooters nemesis.

The one wind location that affects bullet flight most is at the shooter's firing position. And that is best determined and factored into ballistic calculation with a Kestrel/AB 5700 weather meter/ballistic calculator (that has had accurate cartridge and rifle data inputs).
*The above is not an ad for Kestrel/AB, just stating that the instrument is about the best in quickly giving the shooter a very good firing solution.

Two factors that tend to mitigate wind effects may make our bullet choices easier:

1. bullet Ballistic Coefficient- Either in G1 or G7 or both
2. Velocity retention (say every 50 yards/meters)

Generally higher BCs and and how well a bullet carries higher velocities, say to 1,000 yards, will help in overcoming some horizontal and vertical wind effects.

For example: A 180 gr. .300 Win. mag. bullet with a high BC starts out relatively fast but will not carry its velocity downrange as well as, for example, a Berger Hybrid 230 gr, bullet. The 230 gr. bullet is still supersonic after the 180 gr. bullet has gone transonic to subsonic.

Eric B.

 

[HARPERC]

I'm a decent enough shot, but certainly appreciate how much better a good spotter makes me look!

 

[Bullet bumper]

A friend of mine built special gimbaled wind flags that could point up and down as well as all around . It was amazing to see how much the wind was going up and down like a roller coaster when all the other standard flags just showed a single azimuth direction . We tend to think of wind as sheet of parallel air coming across the ground from the one direction . It's not it is more like a wave form , coming in bursts and rolling up and down and swirling around objects at all kinds of angles . The terrain can shape the wind . The wind direction can be completely different at different ranges between you and the target at long range . You can sample all you like at the gun but it could be different down range . You can only do your best to compensate and have a good spotter .

 

[dfanonymous]

This last weekend I was killing some rocks across a canyon and had a wind situation I havn't dealt with before so I wanted to share it. I will start by saying that I shoot a lot in BIG canyon country (central ID), so I am use to shifty winds, updrafts and down drafts. Usually updrafts and downdrafts are expected with the diurnal winds or if the slope lines up with your prevailing wind. Well I set up to shoot across a canyon that was running West to East ( East being down slope), at the head of that canyon is a major ridge running North to South. I had a full value wind coming from the west (coming over that major ridge running N to S) I adjusted for a full value 10 mph wind and adjusted my dope according to the Kestrel and ipad, which have been spot on out to 1700 yds. Broke the shot and watched the shot hit 1 1/2 moa low and 1/2 to the R. I wasn't surprised by the windage being off but the elevation got my attention. readjusted accordingly and broke the second shot. Wind was good and but still 1/2 low. Adjusted accordingly and hit the mark. repeated and hit the mark, realigned on the next pile of rocks at 1625 and repeated the process. This rock required 3 1/2 moa extra elevation to anchor, plus the appropriate wind.

My conclusion, as wind travels over ridges, it creates burbles on the backside of those ridges and down air is the result of those burbles. To back that statement, I was at the same canyon the next day, no wind situation, dialed in my original dope and cold bored the 10x on my rock. Repeated that at the 1625 rock. Something to think about in canyon country.

[ame]https://youtu.be/LdS4njisLzo[/ame]
around the 1100 minute mark is similar to what you are talking about. Cheers.