Magnus Effect

[Meketrefe]

I thought this was a pretty good and fun demonstration of the magnus effect.
So one can see how a spining bullet will be affecting drop when a strong lateral wind is present.

[Liberty's Teeth]

Now we are talking, Meke!
Flow field analisys takes in to account Magnus correct? The yaw of a bullet fired from a RH twist with a 3:00 wind will be different than a 9:00 wind correct? As I understand a 3:00 wind will make the yaw tilt down and a 9:00 tilt up, or do I have that ass backwards?

[Meketrefe]

Now we are talking, Meke!
Flow field analisys takes in to account Magnus correct? The yaw of a bullet fired from a RH twist with a 3:00 wind will be different than a 9:00 wind correct? As I understand a 3:00 wind will make the yaw tilt down and a 9:00 tilt up, or do I have that ass backwards?

One better includes Magnus in this analysis because it is very real. For short distances I would not be too worried but when range increases then it does play a clear role. It is just to make sure we don't forget how many variable intervene in ballistics.
With a Right Hand twist and wind coming from 9 o'clock to 3 o'clock (Left to right) the wind will flow easier on the top along with the rotation and slower at the bottom. That differential will have the same effect as an airplane wing creating an upwards force (lift). So in this case the bullet will shoot higher when distances increase. If the wind was coming from 3 o'clock it would be the opposite. A strong
wind will drag the bullet down over long distances.



One could virtually build an airplane using two light rotating cylinders as wings but those wings have a lot of drag and although they could fly they would not be very efficient. But they will work.

More on the magnus effect.....

https://gfycat.com/ZestyImportantBluefish

[FCG LLC]

Thanks for this. I learned something new today - and it was nothing coming from my wife!

[WARFAB]

There was an article in SSUSA a while back that showed the results of a small bore shooter testing in a cross wind. I can't find the exact article, but this looks like a chart showing the same idea.

Note that the magnitude of this effect is not small. A .308 168 grain Sierra MatchKing at 2,600 fps will experience a vertical deflection of approximately 3/8" at 100 yards in a 10 mph cross wind. Compare that to the almost 1" of horizontal wind deflection that you might be more familiar with.

A left to right wind causes bullets to hit low. A right to left wind causes bullets to hit high. (Note that this would be reversed for a rifle with a left hand twist.) So rather than wind causing a pure horizontal dispersion as you might picture, it actually causes a a dispersion at an angle. The faster your rifle's twist, the greater that angle will be.

Now I don't know about you, but it's hard enough for me to keep track of the horizontal impact of the wind without having to worry about a vertical component. By the way, the angles of the lines on the figure are drawn to scale for a Sierra 168 grain MatchKing with a right hand twist at 2,600 fps at 100 yards.

It's important to note that this effect is much more noticeable at short range than long range. This is because the vertical jump is a constant angle no matter the range, while the horizontal wind will increase greatly at longer ranges. So at long range, the ratio of vertical to horizontal deflection will be smaller - that is, the angle of the line in the above chart will not be as steep at long range.

I highlighted the part in red because this is what always has me scratching my head about the magnus effect in regards to ballistics. According to the magnus effect diagram posted by Meke, a left to right wind should cause the bullet to rise instead of fall. One thing that could explain the difference is that a basketball and tennis ball have rough surfaces compared to a bullet, so the airflow would adhere better to the basketball and tennis ball. Plus, there is obviously the large differences in size.

While basketballs and tennis balls seem to follow the Magnus effect, according to this chart bullets seem to follow Bernoulli's principle, but the article seems to indicate Bernoulli's principle is not the cause of the vertical deflection. If Bernoulli's principle were a factor, the vertical deflection would increase somewhat proportionally with range.

[Meketrefe]

warfab,

As you know things around shooting involve some type of trade off all the time.

This is all relative because it changes with the construction and shape of the bullet, efficiency, speed, trajectory
and in the end because this affects both vertical and lateral deflection. We would also have to take into account
the entire picture through the entire fight path unless one decides this is the best bullet and barrel I need for a fixed range
for score competition. But there is also the practical application.

Magnus alone is going to cause right hand twist to drift to the right and left hand twist to drift to the left regardless of wind.
The magnus force is going to affect stability trying to twist the bullet out of the natural flight path dictated by the center
of gravity and gyroscopic force.

With wind the vertical magnus force is so small that any other variable dwarfs the impact of wind on vertical deflection
or whatever axis always perpendicular to the direction of the wind. So if one has the typical right hand twist the wind from
the right will push on the center of pressure and will help stabilize the bullet faster (down) and follow the natural flight path whereas
wind from the left might fight the path and take longer to stabilize.

In addition there is the force of the air molecules hitting the belly of the bullet as the bullet enters the downward trend in long
range (like the space shuttle landing) and the spin is going to push it even further to the right (or the left for LH twist).

I mentioned the bullet construction and shape because sometimes the longer is the tip of the bullet (like VLD) the longer
is going to be the area of effect and the larger the distance from the center of gravity to the center of pressure and might
be harder to stabilize requiring faster twist rates but at the same time because of their reduced drag they take less time
to reach the target thus less time being exposed to all these forces (including gravity) and the benefits tend to be higher
than the disadvantages.

So all these forces are impacted by the center of pressure that might differ from the center of gravity of the bullet and that
is going to torque your bullet in one direction or another depending on the forces involved and, as I said, even w/o wind.

Increased twist might not be required depending on the shooting but having a faster twist can make a huge difference
in long range to be able to use top bullets and also when dealing with transonic shots because the extra twist will
help avoid the jittery trajectory associated with transonic shots that result in decreased accuracy.

One of the best 168gr bullets is probably the Berger hybrid and nobody should shoot it with less than a 10 or 11 twist.

So I would say there is no better or worse. What one should do however is to get the twist that is needed for the
purpose in mind and following bullet manufacturer and ammunition recommendations.

I think it is good to know what the bullet does but also not to get too worried specially at the distance we normally
shoot in this latitudes.

..
.

ps: and fyi my 300 win mag heavy rifle with the WM match chamber is a 1:8 twist. Crazy? possibly but I want to be able to
shoot the best 230gr vLDs in the market and perhaps one day be able to take it to a place where I can try transonic
shots. The rig is ready for it.

[FCG LLC]

Mek,

Could you all of that again, a bit slower? And possibly in English?

Great stuff. I had to read what you posted 3 times for it to sink in.

LHT

[Meketrefe]

These things are better explained with graphics and videos.
When a bullet goes up in the trajectory the lateral forces are not as big as when coming down because when the bullet starts dropping
faster (accelerating towards earth) the point still points a tad up following the natural flight path. The further is the center of gravity
the better. We can see this clearly in shotgun slugs that have a cup in the back this way the center of gravity moves forward closer to the center
of pressure so they are easier to stabilize that way.

There are so many things going on that it is almost impossible to predict specific things based on constantly changing conditions.
Yet ballistics is one science that is very precise in terms of practical applications and results.
Just look at the precision of naval ordinances that can put a 500lb projectile 30 miles away with pretty precise radious.
Of course with the smart chips in the ordinances that can do small corrections based on GPS they can be dead on that is a huge
requirement in modern warfare to avoid collateral damage.

I am sure you can find materials online and youtube that describe the magnus in all its variants. In terms of lateral variations it
is called spin drift.