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 Extreme Long Range Hunting & Shooting (ELR) Over 1,000 Yds.

# cross winds & downdrafts at 1150 & 1625

#15
05-03-2013, 01:39 PM
 Bronze Member Join Date: Jun 2009 Posts: 87
Re: cross winds & downdrafts at 1150 & 1625

Quote:
 Originally Posted by Idaho Sawyer 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!
#16
05-03-2013, 02:23 PM
 Platinum Member Join Date: Jan 2013 Location: Meridian, Idaho Posts: 1,550
Re: cross winds & downdrafts at 1150 & 1625

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.
#17
05-04-2013, 03:12 AM
 Silver Member Join Date: May 2007 Posts: 268
Re: cross winds & downdrafts at 1150 & 1625

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?
#18
05-04-2013, 06:25 AM
 Gold Member Join Date: Nov 2009 Location: West Texas Posts: 553
Re: cross winds & downdrafts at 1150 & 1625

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.
__________________
" Long distance shooting is an art, often meaning something you have mastered through innate aptitude or long range practice versus a simple application of science" .................Jeff Hoffman
#19
03-24-2017, 10:37 PM
 Junior Member Join Date: Feb 2015 Posts: 3
Re: cross winds & downdrafts at 1150 & 1625

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.
#20
05-09-2017, 02:16 PM
 Gold Member Join Date: Sep 2012 Location: Mojave Desert, Nevada Posts: 885
Re: cross winds & downdrafts at 1150 & 1625

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.
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"There are no comfortable packs, only packs that are less uncomfortable than others."
#21
05-09-2017, 03:09 PM
 Platinum Member Join Date: Jan 2011 Location: Spokane, WA Posts: 3,942
Re: cross winds & downdrafts at 1150 & 1625

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

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