Bullet Climb

[CB900F]

Fella's;

I'm looking for a hard data source to explain a ballistic phenomenon that, so far, is anecdotal.

Several shooters report that if they shoot dead into the wind, using high speed rounds with VLD bullets, the bullet impact is high relative to the target. Somewhere I've read an authoratative article that explains the cause of this, but can't remember where I found it.

The explanation is that there's a lifting body effect across the ogive of the bullet as it rises to midrange. Midrange is thusly elevated over that of the calm day bullet (cdb) & therefore the second intersection with line of sight is extended.

Can anybody help with sources? Thanks

900F

 

[MechAg94]

How many relative feet per second would wind add to the velocity of the bullet?
If the bullet is going 2200 feet per second into a 20 MPH wind, the relative speed of the bullet through the air is then 2230 feet per second. Not a real big difference I would think. Must be something else to it if true.

I'd like to see the article or source if you find it.

 

[MachIVshooter]

Since bullets don't have wings to take advantage of an updraft or air density changes from temperature, etc., gravity wins every time. Altitude (air density) and other environmental factors can affect a bullets trajectory, but will never cause it to climb. A strong updraft could slow the bullets decent, but will not elevate it.

 

[AndyC]

The Magnus effect in external ballistics, also known as 'spin drift'

Another context where the Magnus effect can be found is advanced external ballistics. A spinning bullet in flight is often subject to a sideways wind. In the simple case of horizontal wind, depending on the direction of rotation, the Magnus effect causes an upward or downward force to act on the projectile, affecting its point of impact. Even in a complete calm, with no sideways air movement at all, a real bullet will experience a small sideways wind component. This is due to the fact that real bullets have a yaw motion that causes the nose of the bullet to point in a slightly different direction from the direction in which the bullet is actually traveling. This means that the bullet is "skidding" sideways at any given moment, and thus experiences a small sideways wind component.

All in all, the effect of the Magnus force on a bullet is not significant when compared to other forces like drag. However, the Magnus effect has a significant role in bullet stability due to the fact that the Magnus force does not act upon the bullet's center of gravity, but the center of pressure. This means that there is a Magnus force that affects the yaw of the bullet. The Magnus effect will act as a destabilizing force on any bullet with a center of pressure located ahead of the center of gravity, while conversely acting as a stabilizing force on any bullet with the center of pressure located behind the center of gravity. The location of the center of pressure depends on the flowfield structure, in other words, depending on whether the bullet is in super-sonic or sub-sonic flight. What this means in practice depends on the shape and other attributes of the bullet, in any case the Magnus force greatly affects stability because it tries to "twist" the bullet along its flight.

 

[RNB65]

I don't believe there is an aerodynamic lifting effect. All bullets travel in an arc. If you're shooting into a strong headwind, the wind might well push the bullet into a higher arc than you're expecting, thus causing high hits. Just like a golf ball hit into a strong headwind will balloon up into the air and follow a very different trajectory than a golf ball hit under calm winds.

 

[Eightball]

A strong updraft could slow the bullets decent, but will not elevate it.

Exactly. Sounds like the myth of the "rising fastball" in baseball--it isn't that it rises, it just doesn't fall as much as you would expect it to, and it messes with your brain.

 

[Caimlas]

How much of a change in impact are we talking about, here? A quarter inch at 100 yards? 2 inches? 5? Bullet weight/caliber? Wind speed? Distance?

Here's one possibility, I think. Air, like any other fluid, coalesces and moves about in streams. Depending on precisely where they're shooting from and to, the nature of the terrain, and whether it's a gust of wind, or a constant wind speed.

If you're shooting between two currents, one below and one above, with the one above being faster, I can see how it may alter the bullet trajectory slightly. This makes a little sense, as wind speeds are typically lower near the ground.

 

[Plink]

There's no lift on a bullet. Any force the air applies to the bottom of the bullet would be counteracted by the same force on the top, etc. The fact that it's a very low drag bullet means that it doesn't lose velocity as fast due to air friction (drag). This allows it to get to the target faster, thus not having as much time to drop compared to a bullet with more drag.

As Eightball said "it isn't that it rises, it just doesn't fall as much as you would expect it to".

 

[Titan6]

Sounds like someone had sights set on long range for a short range target.

 

[Hud]

Gents,
For those of you who might be seriously interested in ballistics, I would recommend "Understanding Firearm Ballistics" by Robert A. Rinker, ISBN-13:978-0-9645598-5-1. I picked up my copy at Barnes & Noble for about $25,
or go to http://stevespages.com/zip/canadian_b-gl-306-006fp-001 - 1_june_1992.zip to download a Canadian manual on ballistics & ammunition. It's actually for field artilliary, but the physics is the same, just bigger projectiles.
Regards, Hud

 

[Howard Roark]

I've never read formal research on wind drift. However, many years of Highpower rifle competition proves that head winds and tail winds cause vertical displacement.

Think of it like this: Everyone has held their hand out of the car window and made it pitch up and down like a wing in the rushing wind. The same thing happens to a bullet. I've had up to one minuit's worth of elevation shots due to this. 600-1000 yards. Typically the shot will go high right in a head wind and low left in a tail wind. We call these corner shots. Still in the ten ring if the trigger breaks in the middle.

Nancy Tompkins touches on this in chapter 12 in her book, Prone and Long-Range Rifle Shooting. Nancy and her girls have won more Wimbleton and Leech Cups than any other shooters. Ever.

 

[Zak Smith]

McCoy Modern External Ballistics, pg. 34, section 2.5, "Lift and Normal Forces"

pg. 89, "The Flat-Fire Point Mass Trajectory"

If the total yaw angle is everywhere very small along the trajectory, equations 2.6 and 2.21 tell us that the lift and Magnus forces are also very small, and may therefore be neglected in comparison with the drag force state in 2.1.

 

[the naked prophet]

The magnus effect would not apply. A bullet spins on an axis parallel to the flight path of the bullet, whereas for lift, the spin axis must be perpendicular to the bullet path and parallel to the horizon.

 

[MachIVshooter]

Think of it like this: Everyone has held their hand out of the car window and made it pitch up and down like a wing in the rushing wind. The same thing happens to a bullet.

Bad analogy. Bullets are missiles, not wings. And unless something has gone horribly wrong, they don't pitch and yaw in flight.

 

[Car Knocker]

And unless something has gone horribly wrong, they don't pitch and yaw in flight.

It appears that the folks at Fulton Armory are in disagreement with you:
http://www.fulton-armory.com/fly/fig21.htm

http://www.fulton-armory.com/fly/fig29.htm

For an interesting discourse on how bullets fly:
http://www.fulton-armory.com/fly/

 

[Zak Smith]

There are effects which are technically there, and there are effects which actually affect flat-fire trajectories. That's what the McCoy quote was about.

 

[rockstar.esq]

Interesting concept, although I'm sure that hyper high echelon shooters can and do take such things into consideration. I'm also sure that my attempts at "practical long range" shooting won't require much calculations pertaining to the "Magnus" effect because it'll make such a small difference that I won't likely notice it.

 

[MechAg94]

I like the one explanation above. Wind may push the bullet into a higher arc than planned leading to a higher POI at certain ranges, but overall shorter total distance of flight. Not sure how that would happen with a typical target though. Maybe if you were shooting up hill.

 

[MachIVshooter]

It appears that the folks at Fulton Armory are in disagreement with you:

That is a rather loose application of the word. Oscillate is more appropriate, though I suppose oscillation is more or less a stable and rythmic yaw on two axis. Their diagrams are a bit over-illustrated, as a bullet that oscillates that badly would not remain stable for long.

We know that they oscillate for the same reason that we know rifling stabilizes; imperfections that are negated by gyroscopic stabilization.

Before we get into a debate about the minute details of a bullet's flight, lets consider that the point of this thread is that they simply do not gain altitude relative to initial trajectory, regardless of environmental factors. My point is that a bullet will not nose-up in flight, catch the air current and ascend the way a hand out the car window does.

Edit:

FWIW, at no point in my posts have I made consideration for the destabilization that happens during the transition from supersonic to subsonic flight, at which point bullets can do all kinds of weird things. (though ascending still isn't one of them).

Interesting concept, although I'm sure that hyper high echelon shooters can and do take such things into consideration.

That is why companies such as Corbin have spent thousands and thousands of dollars and hours devloping bullets with long, secant ogives and odd-shaped rebated boattails. Everything they can think of to reduce drag and other environmental factors.

 

[Howard Roark]

There is a bit of truth in most all of these posts. For my bad analogy with the hand in the wind, substitute pencil with hand. The point being that any object moving through a fluid medium will be deflected.

A constant velocity of head wind from muzzle to target cancels out the effect of vertical deflection because it also deflects downward as the bullet travels through its arc to the target.

In the real world the wind is not always constant from one end of a range to the other. Trees, berms and other topography direct wind patterns. A hard head wind while the bullet reaches the apex of its arc deflects it up. If that same wind is not present because it was blocked by trees or hills on its way down into the target it stays on a higher trajectory.

The wind will move in several different directions in 1000 yards. It will roll over berm and tree lines and swirl through bowls on ranges that have deep depressions between firing lines. Roads and power lines cut across ranges make the wind do unpredictable things. Wind flags and spotting scopes are used to see the wind movements. I’ve watched bullet trace make an “S” on the way to the target due to the wind blowing from 3 and 9 o’clock. It canceled out the need for a sight correction.

Nancy Tompkins and David Tubb talk and write about vertical shot displacement. I’ll take their word and my experience that it exists.