Elliptical Swerve

[tbrice23]

I've been trying to read all I can comprehend on gyroscopic stability.

However, can someone tell me in plain English, is the bullet precession only pertaining to the polar ends of the bullet ( meplat and base of boat tail) around the bullets center of gravity?
Or is the bullet's path orbiting around it's true trajectory? Or both?

If it IS orbiting around it's trajectory, is it deviating more than a full caliber? If have read over my answers already I'll have read Brians papers more carefully.

 

[MagnumManiac]

I've been trying to read all I can comprehend on gyroscopic stability.

However, can someone tell me in plain English, is the bullet precession only pertaining to the polar ends of the bullet ( meplat and base of boat tail) around the bullets center of gravity?
Or is the bullet's path orbiting around it's true trajectory? Or both?

If it IS orbiting around it's trajectory, is it deviating more than a full caliber? If have read over my answers already I'll have read Brians papers more carefully.

I have read, but never witnessed, that it can be more than 1 calibre, and looking from behind, or in front, depending on what side of the coin you're on, it would look like the bullet was following a cork screw. It doesn't necessarily oscillate around it's axis, as in wobbling around the tip, like an unbalanced top does just before it falls. The entire bullet is rotating on this abnormal trajectory, but it does settle. This is why MoA can get smaller as range increases, the bullet is rotating tighter on it's axis as it travels further.
Gyroscopic stability is, in the true scientific sense, when a bullet rotates perpendicular to it's centre of gravity axis, and does not deviate from this, but it has been proven due to wind resistance, it can be nose up or down to it's perpendicular axis.
It can get quite complex once you add corriolis effect, altitude etc, etc.

Hope this answers your question.

Cheers.
gun)

 

[Beng]

The flight of the bullet does not follow a cork screw path.
The tip of the bullet makes two kind of cycling motions, a fast and small one and a slow and wide motion. The slower motion varies up to about 4° from the perfectly aligned flight path.

 

[tbrice23]

The flight of the bullet does not follow a cork screw path.
The tip of the bullet makes two kind of cycling motions, a fast and small one and a slow and wide motion. The slower motion varies up to about 4° from the perfectly aligned flight path.

So you are saying that the bullet only oscillates around it's center of gravity??
And not orbiting around it's true trajectory.

Thats what I was visualizing. I cant see a projectile making its way back on path after such deviation. That just doesn't seem logical.

 

[Beng]

The epicyclic swerve is an angular motion of the longitudal axis of the bullet, where the tip of the bullet moves in a circular pattern. It is measured in degree. Wether the center of gravity or the center of pressure is the origin of the motion I don't know for sure, but the center of gravity seems correct to me. The descriptions in "Applied Ballistics for Long Range Shooting" and "Modern Advancements In Long Range Shooting" are pretty good. They should explain everything necessary. I don't have them at hand to quote right now though.

 

[tbrice23]

Thanks for the clarification and reassurance.

 

[BryanLitz]

This is definitely a case where a picture (better yet video) is worth 1000 words:

[ame=http://www.youtube.com/watch?v=KH9SCbCBHaY]Pitch, Yaw and bullet path - YouTube[/ame]

In this simulation, you see the angular motion of the bullet on the left. Think of it as though the bullet had a laser pointer directed out it's nose, and this is the trace it would show on a wall.

On the right is the bullet path from the shooters perspective. Note the bullet starts out below the line of sight (indicated by crosshairs), rises and falls to the zero at 200 yards.

The important thing to grasp here is that the 'swerving motion' of the bullet is much less than 1", a fraction of a caliber in fact.

That's because the coning of the bullet is so fast, that by the time it starts 'steering' to one side due to the nose pointing that way, it's already rotated over to the other side and is now steering the other way.

This happens every several yards so the bullet never steers very far off course.

In summary, there is a 'corkscrew' flightpath, but the amount is less than 1 bullet caliber.

Take care,
-Bryan

 

[Mikecr]

+1 Beng
It's a silly misconception that bullets that have deviated in path will eventually figure out how to correct for this, and then somehow head back over to intended path and group better!

 

[MagnumManiac]

+1 Beng
It's a silly misconception that bullets that have deviated in path will eventually figure out how to correct for this, and then somehow head back over to intended path and group better!

The bullet is not deviating, as the picture shows, if the bullets impact the target at different amounts of wobble, then the group is larger, when they impact with less wobble further down range, the groups are tighter. Deviation is not what this is.
The groups do not shrink, only the MoA shrinks due to longer range.
It is a corkscrew flight path as best can be described.

Cheers.
gun)

 

[Broz]

The groups do not shrink, only the MoA shrinks due to longer range.

I am glad I am not the only one that understands this. Thank you.!! The group size does not get smaller in inches that was measured at 100 yards, but can indeed get smaller in moa down range. I have seen it over and over with larger long bullets in some of my, and other peoples, larger calibers. Proven it so many times I do not need to debate it further. As far as I am concerned it is indeed there and real.

Jeff

 

[Mikecr]

Distant grouping that is smaller in MOA is NOT because bullets are cork-screwing in path.
You're not applying reasoning here.
And, you cannot produce proof of it, not even a credible implication of it.
You have zero basis for the notion.

The term is 'Epicyclic swerve' as simulated by Bryan Litz here:
Notice the actual bullet path as shown on the right pane during this 'wobble' of the TIP ONLY.
That path never steers back to intended, and there is no influence to make it do so.

There is no cork-screwing of bullet path itself, and mere common sense should lead you to this.
It would take a good deal of outside energy, and intelligence, to move a bullet from off path back onto intended.
Such a condition can be present with rockets -but rockets fly and we fly them.
Bullets do not fly -they simply fall.

The common cause of all this yaw is ugly bullet release. The common cure is a precision crown, reduced muzzle pressures, and perpendicular bullet base(flat base). As far as the number of bullet rotations to damp out what yaw you're causing, this is a matter of adequate stability to do so.
Nothing about pitch and yaw are good for our results, as the detriment from it is lasting to the bullet's fall.

 

[CB11WYO]

Subscribing for later contemplation...

-Clint

 

[Mikecr]

[I had not noticed that Bryan posted earlier]

The bullet is not deviating, as the picture shows,

That's correct

if the bullets impact the target at different amounts of wobble, then the group is larger,

Probably, as different yaw and pitch between shots amount to errors that we pay a price for.

when they impact with less wobble further down range, the groups are tighter.

This is where you've lost the whole concept of what's happening.
There is no correction to errors imparted earlier. Those wobbling bullets that provided bad results earlier, also provide bad results later.

Deviation is not what this is.
The groups do not shrink, only the MoA shrinks due to longer range.
It is a corkscrew flight path as best can be described.

You're contradicting yourself all over the place here. Further departure from the concept of what's happening..

 

[CB11WYO]

...In summary, there is a 'corkscrew' flightpath, but the amount is less than 1 bullet caliber.

Take care,
-Bryan

Mikecr,

To clarify my interpretation of your thoughts, do you or don't you agree with this statement from Bryan? ^^