Shooting across canyons/ bullet drag

[WKR]

Yesterday while shooting a few mock nrl hunter stages we set up, me and a buddy were noticing that at the far targets our shots were trending high.

At first when the wind was sub 10 mph right to left we both had to adjust 0.2 down, later in the day when the wind picked up it was as much as .4-.5

Now, both of our rifles/loads have been trued and there was no doubt in either of our systems inputs or zeros, so we make sure pressure/ DA was true with a kestrel and again it was correct.

The only other explanation is the terrain. The far targets were across a steep canyon that had a significant vertical updraft.

We both have shot across canyons many times, but in this terrain it had the most notable effect. It's a long valley, and this canyon ridge is the first wind break coming up from the valley floor. So I'm thinking that without any other features to create turbulence or slow the wind down, that updraft is pushing the bullet travel upwards significantly.

Sub 650 yards, the effects were marginal, but once we got out to 800 and beyond it was substantial.

Anyone else experience this updraft on bullet flight when shooting over steep canyons? I'm used to horizontal winds doing weird things over canyons and in mountainous terrain, but the vertical aspect had never been as pronounced as it was for us yesterday.

It was good though, I like learning these things while practicing and training, as it really makes me think about my limits on game depending on environmentals

 

[hereinaz]

Yes, wind flows like water. Wind going up a hill/canyon has as much effect as if it were blowing from the side. The hill angle and your angle means it won’t be a full value wind, cause it will be coming in at oblique angle.

And, as right to left wind you got a little aerodynamic jump at 850 as well.

 

[Brucebarker024]

Funny enough I and others I hunted with this year experienced this on 3 animals. All across canyon downhill, between 4 and 600 yards. I was not the shooter for any of them but everyone said they aimed top of the bottom third of the body and 2 were high shoulder cns hits and the third was a spine shot that required a follow up.

 

[hereinaz]

Wind also is compressed as it has to go over a hill, so a 10 mph wind in the valley becomes more as it compresses to get the same amount of air/wind over the hill.

 

[hereinaz]

Funny enough I and others I hunted with this year experienced this on 3 animals. All across canyon downhill, between 4 and 600 yards. I was not the shooter for any of them but everyone said they aimed top of the bottom third of the body and 2 were high shoulder cns hits and the third was a spine shot that required a follow up.

Yes. It doesn’t take much to push the bullet up. You guys must shoot enough to be able to make those shots and stay in the body.

I like to shoot low, because errors almost always seem to be high. I also take out a .1 or .2 when I dope a rifle for other shooters on my rifle.

Often, shots that would be perfectly centered up on a range end up high in the field because of this effect. More common is the effect of recoil in field positions. It’s hard to tease it out if you aren’t the shooter and know your rifle.

 

[Wrench]

If you're shooting n/s across a east facing canyon in the warming hours, you can expect some thermal effects. The west and and north faces will do the same, but a bit later in the day.

The diurnal thermals are pretty predictable....but it takes exposure to figure them out.

As mentioned the ridges create eddys and currents much like water. A west to east wind hitting a N/S draw is going to have a pressure event on the east side.

A way to diagnose the wind is to use your parallax or binos and try to focus on the air or terrain on the trip.

 

[hereinaz]

You gotta guesstimate the actual wind and the angle. With compression of a 10 mph call it 15-18 mph full value and the angle 30 degrees…

Also, the higher you go above the ground the faster the wind.

Blue bullet
Yellow wind
Red hill
Purple wind angle

 

[Wrench]

Your wind direction will also cause the bullet to climb up or crawl down from its spin.....a rh twist into a 3 o'clock will climb....a 9 o'clock will crawl.

 

[hereinaz]

Your wind direction will also cause the bullet to climb up or crawl down from its spin.....a rh twist into a 3 o'clock will climb....a 9 o'clock will crawl.

Yup, aerodynamic jump is the technical term. I like the climb or crawl visual.

 

[Dave_S]

I think this is a great example of why guys shouldn't be taking long shots if they don't have the opportunity to shoot in these conditions regularly. Saying this as a guy who doesn't get to shoot in these conditions.

 

[Fireflyfishing]

The time of day will have an effect as well.

 

[SloppyJ]

If you're shooting n/s across a east facing canyon in the warming hours, you can expect some thermal effects. The west and and north faces will do the same, but a bit later in the day.

The diurnal thermals are pretty predictable....but it takes exposure to figure them out.

As mentioned the ridges create eddys and currents much like water. A west to east wind hitting a N/S draw is going to have a pressure event on the east side.

A way to diagnose the wind is to use your parallax or binos and try to focus on the air or terrain on the trip.

Diurnal.... only heard that one other time... in large scope sewer studies. Just interested where you picked that up. It's odd to hear it used correctly other places for me.

 

[Wrench]

Diurnal.... only heard that one other time... in large scope sewer studies. Just interested where you picked that up. It's odd to hear it used correctly other places for me.

I picked it up in my "how to be a redneck" class....lol.

It came from Valurius Geist's teachings of elk and elk ecology.....iirc.

 

[Wrench]

One thing that also gets completely messed up is wind values. Full value is exactly that, 90*.

When the angle changes, the value or correction required changes quickly.

Here's a page from my DOPE book that will help you.

 

[Wrench]

In case the resolution sucked....

 

[MEdude]

A way to diagnose the wind is to use your parallax or binos and try to focus on the air or terrain on the trip.

Guessing you mean looking at the mirage at mid-distance(s) between you and the target.

If so, how do we estimate wind value as the mirage effect may look like a 45° angle (arbitrary value), but wouldn’t that be because the air is moving at a 45° upslope with an unknown speed?

East coaster, desperately trying to learn wind.

 

[hereinaz]

I think this is a great example of why guys shouldn't be taking long shots if they don't have the opportunity to shoot in these conditions regularly. Saying this as a guy who doesn't get to shoot in these conditions.

Yes, it is important to shoot in the conditions.

The longer the shot on an animal, the better the conditions need to be even for me. Fortunately, in AZ, many times the wind slows to a calm condition as the sun goes down or comes up.

 

[Steve300xcw]

Guy can learn a lot by watching the fog/clouds move around.

 

[hereinaz]

Guy can learn a lot by watching the fog/clouds move around.

Yes. We don’t get a lot of low fog and clouds here in AZ where ai do a lot of shooting.

Best reading on the subject is for wildland firefighting.

Another helpful tool for analyzing the prevailing wind up above the ground is the app called Windy. Use it to imagine the direction and speed up above the terrain, then look at what direction and speed the land features are pushing the wind at the ground.

A kestrel helps you with local wind speed, but typically whatever wind you’re feeling seeing on one side is going to be different on the other unless the wind is rushing down the canyon in line with the canyon and ridges, which rarely happens.

Imagine shooting from a finger ridge across another finger ridge and two draws where they come together. 800 yards gets impossible to gauge because of wind flowing and changing directions.