Bullet drop depends on left/right wind direction?

[TotallyClueless]

I've been playing around with the Hornady ballistics calculator on my phone (standard BC feature, not 4DOF) and noticed something strange. Wind from 90 degrees right results in significantly less bullet drop than a calm wind scenario. Conversely, wind from 270 degrees left results in significantly more bullet drop than a calm wind scenario.

For example, my 127 LRX load in 6.5 CM, 100 yard zero, 300 yard shot...

No wind: 12.9" drop
10 mph, 90 degrees: 10.5" drop
10 mph, 270 degrees: 15.1" drop

That's a significant difference in trajectory just based on left/right wind direction at a modest distance. This is seen across the board with every load I try in the app. I've never observed this effect in real life and haven't found any posts discussing this part of the Hornady ballistics calculator. Do you guys have any experience with this effect or anomaly in the app?

 

[Antares]

Do a little Google reading on "Aerodynamic Jump." The difference in wind direction is due to the rotation and yaw of the bullet in flight.

I'm not smart enough to explain it.

 

[ozyclint]

Magnus effect?

 

[wind gypsy]

Do a little Google reading on "Aerodynamic Jump." The difference in wind direction is due to the rotation and yaw of the bullet in flight.

I'm not smart enough to explain it.

This. I'm not familiar with the aerodynamic jump function of the hornady app but i'd guess that is probably what is causing this. Other apps do it too.

I was taught that it is frequently overstated by solutions in applied ballistics but it is definitely a real thing. They discussed this on a recent VP precision podcast where the wind changed 180 degrees on subsequent stages and caused the elevation dope to change by 0.4 mil.

 

[TotallyClueless]

Interesting stuff. I'm really not as surprised that the effect exists, but that it should have such a significant effect according to the Hornady app. Perhaps the app is overstating it like you mentioned, wind gypsy. One of these days I'll have to get out on a nice big piece of BLM land and test it out, shooting both directions with wind direction as the isolated variable.

For reference, how much of an effect are you guys seeing at 300 yards with your preferred load(s)?

 

[Antares]

This is what the Hornady BC Calculator gives me for my 6.5CM (140 ELD-M) @ 300 yards.

No wind: 4.04 MOA drop
10 mph, 90 degrees: 3.28 MOA drop
10 mph, 270 degrees: 4.79 MOA drop

 

[BWB]

Aero jump is very real, as others have already posted and shown results. Most Phone App solvers "didn't use to" account for this. I know Applied Ballistics is one that does have it enabled. The wind will most definitely affect elevation and magnified the further the distance.

 

[Turkeytider]

When one considers the myriad of things that can apparently impact the travel of a bullet from point A to point B, sometimes it`s amazing to me that we can hit ANYTHING at ranges over 200 yards! For me, sometimes at the range while shooting at 500 yards, I swear every ......single...... one of those factors is in play!

 

[hereinaz]

Magnus effect?

No, magnus effect causes spin drift to the right on right twist barrel.

“Precession” which is the spiral shape the tip traces like many tiny repeating four leaf clovers in a circle. Wind causes instability and the wind creates instability. It then moves up or down depending on the direction the wind comes, causing causes the bullet to jump or drop. That’s aerodynamic jump.

As the bullet gets knocked off its path, gyroscopic forces stabilize it, if hit from the wind right to left it will go higher because the nose stabilizes pointing higher. If it get hit the other way, the bullet stabilizes with the nose pointed down.

 

[hereinaz]

This. I'm not familiar with the aerodynamic jump function of the hornady app but i'd guess that is probably what is causing this. Other apps do it too.

I was taught that it is frequently overstated by solutions in applied ballistics but it is definitely a real thing. They discussed this on a recent VP precision podcast where the wind changed 180 degrees on subsequent stages and caused the elevation dope to change by 0.4 mil.

The ELR shooters I know use Applied Ballistics because those things matter.

I don’t know that most shooters are competent enough to shoot and know the cause of any particular error. It’s why comparing ballistic solutions solver to solver doesn’t help.

And, if people shoot at the same shooting range, with similar prevailing conditions, they won’t see it. Or, when they start missing because of the wind change, they will usually look to the things that they know of, and blame it on any number of things. Or, just ignore it.

 

[hereinaz]

Interesting stuff. I'm really not as surprised that the effect exists, but that it should have such a significant effect according to the Hornady app. Perhaps the app is overstating it like you mentioned, wind gypsy. One of these days I'll have to get out on a nice big piece of BLM land and test it out, shooting both directions with wind direction as the isolated variable.

For reference, how much of an effect are you guys seeing at 300 yards with your preferred load(s)?

At 300 yards the effect will be small with most any bolt action centerfire cartridge with velocity. The faster a bullet, the less the effect, and the shorter the distance the less the effect.

You won’t miss at 300 because of aerodynamic jump. The wind speed necessary to cause enough jump is going to be shaking the rifle and drift will be massive.

 

[8404]

This is caused by gyroscopic precession. Basically, if an object is spinning, any force exerted on that object will respond 90 degrees from the direction of input.

The bullet is spinning somewhere in the neighborhood of 250,000+ RPM.

If the bullet is spinning clockwise, because the barrel has a right twist, wind hitting the bullet from shooters left, imparts a force to the bullet on its left side. 90 degrees from that point is straight down, so the bullet drops.

If the wind hits the bullet from the right side, 90 degrees from that point is up, so the bullet will climb.

So whatever your elevation correction is with zero wind, you will have to add LESS elevation with a right to left crosswind (because the bullet is climbing due to gyroscopic precession) and MORE elevation with a right to left crosswind (because the bullet is dropping due to gyroscopic precession.)

 

[hereinaz]

This is caused by gyroscopic precession. Basically, if an object is spinning, any force exerted on that object will respond 90 degrees from the direction of input.

The bullet is spinning somewhere in the neighborhood of 250,000+ RPM.

If the bullet is spinning clockwise, because the barrel has a right twist, wind hitting the bullet from shooters left, imparts a force to the bullet on its left side. 90 degrees from that point is straight down, so the bullet drops.

If the wind hits the bullet from the right side, 90 degrees from that point is up, so the bullet will climb.

So whatever your elevation correction is with zero wind, you will have to add LESS elevation with a right to left crosswind (because the bullet is climbing due to gyroscopic precession) and MORE elevation with a right to left crosswind (because the bullet is dropping due to gyroscopic precession.)

Excellent explanation. I like it. You said it, and to make it clear, the 90 degree turn is in the direction of the spin. So picture clockwise 90 with our right twist barrels.

The same thing goes for a downdraft and vertical wind. It will move left or right, respectively turning clockwise. Shooting long range in a canyon that has strong winds will do strange confusing things unless you know some of the reasons. Of course, the wind angle and distances with wind blowing from above or below are not as pronounced as a cross wind. But, at extended range when a bullet is slower, it can happen.

 

[Turkeytider]

At 300 yards the effect will be small with most any bolt action centerfire cartridge with velocity. The faster a bullet, the less the effect, and the shorter the distance the less the effect.

You won’t miss at 300 because of aerodynamic jump. The wind speed necessary to cause enough jump is going to be shaking the rifle and drift will be massive.

What about 500 yards? Should one expect aero jump at that range ?

 

[8404]

Aerodynamic jump is happening at ALL distances if there’s wind present. Using a ballistic app like 4DoF will help you start understanding this. Get a Kestrel (just a simple one that will give you wind, temp, barometric pressure, and humidity) and start using it every single time you’re at the range, or even just take it for a walk and play with it.

If you’re hiking sit and think about the wind and try to visualize what it’s doing. Then pull out your kestrel and see what it says.

Plug that information into your (free) 4DoF app and then put everything it tells you into the context of what it would mean if you have to make a shot at that moment.

You can do a lot of “practice” without ever firing a shot.

 

[Turkeytider]

LOL! One thing is for certain! After reading about precession....aerodynamic jump...and everything else impacting bullet flight, I have a new appreciation of rifle shooting and will absolutely REVEL in each and every occurrence in which a bullet that I`ve shot actually makes contact with the 6" target I shoot for at the range at 500 yards. Those occasions that find me actually hitting the 4" ? Savored like fine wine!!

 

[Formidilosus]

What about 500 yards? Should one expect aero jump at that range ?

You are not missing due to AJ. Do not get mired in minor irrelevancies. You/we miss because-

- we suck
- scope doesn’t work correctly
- missed called wind

In that order.

 

[Wrench]

Here are two pics that I was able to grab from a range session on a windy day. You can see the bullet yaw into the wind. There was a 15+ breeze that day.

 

[Marbles]

Excellent explanation. I like it. You said it, and to make it clear, the 90 degree turn is in the direction of the spin. So picture clockwise 90 with our right twist barrels.

The same thing goes for a downdraft and vertical wind. It will move left or right, respectively turning clockwise. Shooting long range in a canyon that has strong winds will do strange confusing things unless you know some of the reasons. Of course, the wind angle and distances with wind blowing from above or below are not as pronounced as a cross wind. But, at extended range when a bullet is slower, it can happen.

Is that clockwise from the shooters position (looking at the back of the bullet) or from the target position (looking at the tip of the bullet)?

 

[8404]

Is that clockwise from the shooters position (looking at the back of the bullet) or from the target position (looking at the tip of the bullet)?

That’s from the shooter’s perspective