bullet above bore's axis...?

Alaninga said:
...will put this post to bed, unless any additional thoughts need posting : )

Unless someone does some testing in a strong crosswind with a 'well known behavior' bench gun that wants to show us all something when tested in a strong crosswind, either side!
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Testing conducted 1/5/2009 in the middle of an open field with a rotating bench.
Two targets and the bench were set up with the wind perpendicular to course of fire.
25 shots fired at 279 deg's and a second 25 shots were fired at 99 deg's using a competitive BR rifle chambered in 22lr.
4 Electronic wind sensors located along course of fire recorded a wind that varied from an average on target #1 of 6.9mph with one recorded gust to 10.6mph, to target #2 with an average of 6.1mph with a recorded gust of 8.9mph.

The results: Nearly identical to ballistic theory for "Aerodynamic Jump" when calculated by using the Sg (Stability factor) derived from twist rate, velocity, and the physical length of the projectile. Edit: The Miller equation was tweaked by me with the use of a subsonic factor to correct for 22lr ballistics.
Further explanation: The vertical deflection occurs in the first few precession cycles after the bullet enters into a crosswind and is forced to realign its axis with the oncoming air flow. In other words, as the bullet is torqued to weather-vane into the wind, it sets up a gyroscopic action (Right Hand Rule for simplicity), which results in the bullet being deflected down when its axis is torqued by a left-to-right crosswind and vise versa. (Right twist barrels only).

Landy

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Winds_zpsb7af0ad8.jpg
 
I find all this interesting but not so sure this test proved the bullet rose above the bores axis. It seems it just proved the bullet hit higher or lower than the point of aim. The wind can affect its flight. Picture this test with a horizontal barrel and very close range. The bullet starts dropping immediately, you would need a whole lot of wind in whole lot of hurry to make the bullet rise or maybe a really fast bullet.
 
sdean said:
I find all this interesting but not so sure this test proved the bullet rose above the bores axis. It seems it just proved the bullet hit higher or lower than the point of aim.
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You're correct. This test did not prove anything of the sort, and wasn't meant to.

Landy
 
No, no, no,,,

,,,, please don't 'put this thread to bed' yet! :( It's just now getting interesting! :cool:

Alaninga, I want to congratulate you for opening one of the most interesting BR Central threads seen in quite some time. :D It has attracted the attention of many of the most brilliant minds that frequent BR Central and reveals more than one misconception that exists even among the experts. It also sheds some light on something I have been trying to completely understand for several years and that is how gyroscopic forces cause a bullet from a right hand twist to drift left and up/right and down. :confused:

Some time ago, (probably several years the way time flies :rolleyes:) we had a most interesting discussion here on the forum about this very subject. Based on personal experience with gyroscopic forces in another life, I was of the opinion that the 'experts' were wrong. :mad: Imagine that! Me,, a redneck from West Texas, questioning the likes of Berger's ballistics chief, Brian Litz, a former Air Force rocket scientist. :rolleyes: Well as it turned out, Brian was mistaken and I was right! :eek: :rolleyes: But wait! :eek: That's not the whole story. :rolleyes: If you are interested in hearing "The Rest Of The Story" let me know and I'll do my best to explaln.

In the meantime,,,,,if you have a Dremel Moto tool, get it out and play with it a bit. Notice how it behaves gyroscopically. :) Turn it on about half speed and hold it out horizontal between your thumb and forefinger. Now twist it to the right. Which way does the nose go? Brian Litz was surprised too. :eek: I'll never forget what his response was when he tried it; it was so funny . :D Brian said, "My whole world fell apart!" :eek: Remember Brian? Oh we had some good exchanges over that. I have not yet had the pleasure and honor of meeting Brian face to face but I'm sure looking forward to doing so. Guys, Brian Litz is the real deal!

Later

Gene Beggs
 
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Apply simple vector analysis of a bullet in a 10 mile an hour wind and compare that to what you know from observation at the range in competition or not. When I first started shooting short range I set down and did this. The bullet moves no where near the mass of wind it's in moves. Then the gyro stuck out it's ugly head. Stability from the gyroscopic action explains this (at least to me). I certainly maybe simplifying when I talk about gyroscopic precession. I admit I do not know the math. In my mind it explained it though. Force applied to gyroscope manifests itself 90 degrees from where applied. It makes sense to me that a 90 degree crosswind from right with a right hand twist barrel causes bullet left and up. This is empirical for anyone who shoot bench rest especially short range because can be easily checked on sighter. Now as to original question, NO! the bullet does not rise above axis of bore, can I prove it? No I can not, but I bet this thought arises from the numerous diagrams, pictures showing bullets arcing up at the exit point of barrel. Here's a website that may answer it.(http://www.chuckhawks.com/bullet_trajectory.htm) Look at diagram below Heading: Typical Alignment.
Another website (http://www.centerfirecentral.com/articles/traj.htm)

Bill Greene from sunny Arcadia, Florida.

seventy degrees tomorrow!!
Might have to start fire forming for next year with this great weather we are having! I
agree with Gene keep this thread going it is a lot ofun!
 
I've always liked the concept of the bullet spin climbing an oncoming wind though I wonder how much grab a bullet can get in a partial vacuum created by the sound barrier shock wave. I know they had some surprises with the way planes control surfaces worked after the sound barrier was passed and they had to redesign them.

I also wonder how much the bullet precession controls the drift. Maybe it is time to go beyond tunnels for testing and get a rifle up on the International Space Station where we can really work up some data.

Sorry if this has been touched on. I read a bunch of the post in the beginning and went away with some of the post haunting me. I haven't caught back up yet.


P.S. I may have used the wrong word when I said precession above. What I meant to say was maybe the gyroscopic effect has a lot more bearing on where the bullet is than we give it credit. Maybe it has such an effect that it stabilizes it where its at and it is the rest of everything that is allowed to walk away from it.
 
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Gene Beggs said:
,,,, please don't 'put this thread to bed' yet! :( It's just now getting interesting! :cool:
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It's great to see you jump in on this Gene! All the talk about the respected ones leaving BRC had me wondering how bad it really was. I see hope.

If you could, I for one would be interested in hearing "The Rest Of The Story". I wasn't around when that discussion was had. I just did your dremel test and I'm most puzzled.
 
A gyroscope wants to stay where it is. Go to dime store buy one play with it. Dime Store? Damn if I ain't giving my age away.
Bill Greene
 
Learned a new acronym

Alaninga; Let's sum it all up as....DMA said:
Alan, I just love acronyms. :p Your DMA is one I had not heard before and it so perfectly describes so many things that we obsessive compulsive types fret over. :rolleyes:

Many of us are just not satisfied with knowing what happens we also want to know exactly why and how it happens. We know that bullets from a right hand twist barrel drift left and up as a result of a right to left crosswind. Vaughn, McCoy, Litz and other ballistic experts tell us the vertical is due to gyroscopic forces and we would probably be well advised to accept that as the truth it is and go on about our business and worry about more important things that really make a difference. :rolleyes: Like how to read wind flags, how to keep a rifle in tune etc, ,but,,,NO, some of us just gotta' keep studying for sometimes years trying to figure out exactly how something works.

I'm sure many world records have been set and national championships won by shooters who knew little or nothing about exterior ballistics and didn't care. DMA :) That's right, it doesn't matter anyway; they were simply experts at rifle handling, knowing where to hold, when to start a group, when to stop, when to go to the sighter etc. In depth study and understanding of some things is interesting and satisfying but; will it help you shoot better in competition? Nah. :rolleyes: :cool:

But it's fun isn't it? Stick around guys, we'll figure all this stuff out one of these days.

Later

Gene Beggs
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About this recoil thing...

I am sure that I am not the only one who has seen this.

I shot a deer at about 540 steps, which must have been every bit of 500 yards, many years ago. This deer was in a plowed field and I was on the top of a hill shooting from a prone position. The first shot was low in the dirt even though I had aimed high. I saw the bullet hit the dirt before the recoil caused me to loose sight of the deer. I adjusted and hit the deer. The point is that I saw this in my scope before the recoil had raised rifle.

Forget about me getting the deer at such a long range. I don't believe the recoil effected the point of aim in the least if I could see the bullet hit at over 1/4 of a mile before the recoil had an effect. It must have been an inertia thing.

What do you other experts think about that?:)
 
Happy Thanksgiving everyone. :D

I'm going to stay off the computer today so I can spend more time with family and friends but I promise to get back to you tomorrow.

Have a great turkey day!

Later,

Gene Beggs
 
Dusty Stevens said:
Bullets go above the bore's axis for quite a while until it reached the point blank range which on some cartridges can be quite far like 200+ yds
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Not likely:
They do go above the center axis of the scope for quite a while in the scenario you are envisioning.
 
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Oops!

Joe Woosman said:
Alaninga, I assume your question relates to a wind from right to left on a right hand twist barrel seems to push the bullet higher on the target relative to no wind. This has to do with the gyroscopic forces of the spinning bullet. The nose of the bullet turns into the wind and upward creating lift.



Joe, you were the only one that expressed interest in hearing "The Rest Of The Story" so here goes;

Like you, Bryan Litz was mistaken when he said exactly what you did above and I quote,

"a wind from right to left on a right hand twist seems to push the bullet higher on the target relative to no wind. This has to do with the gyroscopic forces of the spinning bullet. The nose of the bullet turns into the wind and upward creating lift."

You are correct in everything you say above with the exception of which way the nose goes when it reorients itself to the right aligning itself with the new relative wind. In the example above, the nose of the bullet will go DOWN not up. This was the reason I came up with the Dremel tool demonstration.

Intuitively what you and Bryan erroneously believed makes sense and would explain why bullets drift left and up in a right crosswind and we all know that's exactly what happens but it's not for the reasons you and Bryan stated; if it was the bullets in the example above would drift left and down, not left and up.


"So Beggs" if what you say is true then what in 'ell is it making the bullets drift left and up?

Beats the 'ell outta' me! :rolleyes: I've been trying for years to get my head wrapped around this. :p I have not had the chance to get with Bryan in person but that's what it will take to get it figured out. Discussing something this complicated by keyboard is too much for an old redneck from west Texas like me.

I suggest you get your Dremel tool out. The armature turns clockwise like the bullets in the example above. Grasp the Dremel between your thumb and forefinger right at the center of gravity so it pretty well remains horizontal but is somewhat free to rotate up and down when you twist it to the right like the bullet must do in a right crosswind. Have fun! Don't let it drive you crazy. Maybe between you, Bryan and myself we can figure this thing out.

Good luck

Gene Beggs



PS: I sure like Alaninga's acronym DMA (doesn't matter anyway)

So much of this stuff we OCD types obsess about DMA. :rolleyes: But it's fun; isn't it? :cool:
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Oh,, what a diabolical question!

Alaninga said:
I know for all 'practical' physics that a bullet drops below a bore's axis as soon as it leaves the barrel. IF a wind [strong?] is coming from the right, and the bullet is spun in a right handed twist bore, will it rise above the bore's axis a small amount? Or will the right crosswind's effect only 'slow' it's fall compared to a 'no wind' shot?
: )
Really, probably discussed a million times, but I wasn't listening :)[/QUOTE



Alaninga, you sneaky rascal :mad:

You must understand this ballistics stuff very well to even ask such a question. You knew that throwing this little loaded bomb of a question out to us old nit picky retired guys would initiate a lively discussion; didn't you? :mad: Sure you did, but it's all in the name of fun and continuing education; huh? ;)

Later

Gene Beggs

I just love your acronym, DMA (doesn't matter anyway)
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Gene Beggs said:
Like you, Bryan Litz was mistaken when he said exactly what you did above and I quote,

"a wind from right to left on a right hand twist seems to push the bullet higher on the target relative to no wind. This has to do with the gyroscopic forces of the spinning bullet. The nose of the bullet turns into the wind and upward creating lift."

You are correct in everything you say above with the exception of which way the nose goes when it reorients itself to the right aligning itself with the new relative wind. In the example above, the nose of the bullet will go DOWN not up. This was the reason I came up with the Dremel tool demonstration.
Click to expand...

Thanks for the follow-up Gene.

Over the Thanksgiving festivities the last few days I've been giving this a lot of thought. I had to go back and do some studying to try and find the error in my thinking. I THINK I've got it corrected now but I must admit I have to rely a LOT on the work of others, particularly in the math department. The Ruprecht Nennstiel "How Bullets Fly" page is the most comprehensive and easy to absorb work I have found so far.

With a right hand wind/right hand twist, the bullet nose up and yawed to the right explains the effects seen on the target. A gyroscopically stable bullet must correct course into the wind or it would not be stable. If it pointed nose down we would not see what we do on the target. This is why it was so disturbing doing your Dremel test. Indeed if you turn the Dremel to the right in dives nose down!

After reviewing my materials, I believe the bullet really does end up exactly as I stated, (nose up and to the right), but how it got there was not covered. The math says a wind force from the side applies its force to the center of pressure. The center of pressure on a typical bullet is forward of the center of gravity, (closer to the point of the bullet). This force applied at the center of pressure turns the nose of the bullet about its center of gravity. So if you hold a bullet, or your Dremel, in the center and apply a force from the right near the point of the bullet or the cutter on the Dremel, it turns to the left!!

The gyroscopic forces then resists this change causing a yaw motion up. This is easily felt with your Dremel test. The bullet nose begins to oscillate in a conning motion until it becomes gyroscopically stable again pointing into the direction of airflow. This is called gyroscopic precession.

Many years ago I studied this stuff and I did have this understanding. I believe the motion between stable in no wind and stable in right wind was lost in the DMA (doesn't matter anyway) of bullet flight. Just accepting the nose up and to the right explains what is seen on the target.

I would add this this lost motion probably helps explain what Landy observed in his test where there was a greater wind effect where the bullets entered the wind.

Good stuff!
 
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