Brent,

You're way too kind! Seriously, thanks ever so much... I mean that.

I don't expect that even the most celebrated of thinkers isn't wrong every now and then. And if they can be wrong, laymen like me must be wrong plenty more often ... So I promise to be the first to admit it if my "massacred snowman" theory of muzzle movement starts "melting." I'm not an engineer like Harlod Vaughn, but it's good to see I'm not totally soaked in every respect...

Thanks, too, Brent, for going to the trouble of entering all of that text from Vaughn's book. I think you've sold another copy for him--I'm going to buy it. I am generally skeptical of too much "egg-headery" in these types of matters, but when Vaughn says: "Now a note to the reader: this chapter is one of the longest and most complex in the book. However, every effort will be made to explain everything in physical terms so that the information should be clear to the reader without a technical background. So, hang in there!" he wins me over heart and soul. He would likely agree with one of my favorite rules which is "If you can't explain it in layman's terms, you don't understand it!"

A friend from snipershide.com , Blaine Fields, has shared some more of the text with me, and I've read other excerpts elsewhere. So again, while initially skeptical, I'm going to (primarily on the merits of the very refreshing approach of "keep it simple" for the masses) purchase the book.

Take care to all,

Dan

HC...

Nice try, but, as usual, you missed the point, miserably I should add...

My point is, when I do not know something, I ASK FOR INPUT instead of bragging, but probably this is asking too much for your ego.

As Brent, explained perfectly... you are making a fool of yourself...

I've been watching this thread and have found it quite entertaining...thank you all!

HotCore, I don't think you need to invest in all that. I think it's more efficient to take advantage of the work that others have done in that area. Here's a couple of references for you (aside from Vaughn's barrel mounted accelerometer work).

Cranz and Koch of Germany did the first really scientific studies on rifle vibrations back in the early 1900's. The methodology and results are recounted in "Textbook of Small Arms". Their testing was done in just the vertical plane.

Capt Philip Quayle did some extensive work on barrel vibration which was published in the January 1927 issue of the American Rifleman.

The arsenals and labs did/do a lot of testing in this area, but unfortunately the results are rarely published.

Green788 when you say...

quote:

---

Countless articles and books on rifle accuracy over the years have all dealt with the physics of the barrel's vibrations.

---

Can you provide references that I can chase down?

Harold Vaughn, programmed the computer modelling for barrel vibrations and experimentally validated this model. He further tried to minimize barrel vibrations by eliminating the sources at the receiver. His recounting the process with successes and failures included makes for fascinating reading.

Through the whole thread, I like this quote from Art S the best;

quote:

---

I really believe that what draws all the criticism and causes the rift is the constant need to attach some psuedo-theory to what is observed. Just concentrate on the development method and forget the theory, which is much to complex to elucidate by study of a few shooting books and shooting at a target. I think a lot of people can benefit from a consistent load development method. What I see however, are posts from beginners prattling on about whether someone thinks their barrel is going through a high or low acceleration phase of its vibration pattern at a given loading. They are missing the whole point which could help them, which is be consistent, home in on results and change one thing at a time based on results.

---

[ 03-06-2003, 01:34: Message edited by: Chris F ]

Well... I'm a firm believer in the "two heads are better than one" idea.

When we all get together here, kick around some ideas and compare notes, I believe we all learn.

I don't think it is a bad idea at all to share speculations. It's fun, actually (And even Art didn't resist the invitation to do the same )...

Chris, the items I've seen over the years are blurry archives these days, and the sources don't come quickly to mind. But I think most of us have seen the "twisted ellipse," or "figure 8" depiction advanced as truth. This pattern is fairly ubiquitous, and it simply makes good sense, if you think about it.

Think about it this way: No one denys the existence of "nodes" in the vibration whip. If there is one node, there will be an opposing node. So while there may be many secondary, less significant nodes, there will be two main nodes in the vibration path. And one of these two nodes is what we try to "pin down" with good handloads, or other techniques. The shape of the muzzle's path would seem important only at that critical moment when the bullet is about to free itself of the bore--anything that leads up to this is curious, but unimportant, or so I'm inclined to think. Further, the liklihood that one node is on one side of the static point of the barrel, and the other node on the opposing side would be a given. (The muzzle can't vibrate in only one direction). So when you really begin to think about it, you keep coming back to something like the "pinched" ellipse, or figure 8.

It would be interesting to consider further arguments (the gentlemanly type!) as to why the vibration would be different than the twisted ellipse, such as what Art advanced...

But that's just my opinion.

Dan

Green788,
I've never seen the "figure 8" vibration pattern advanced in any credible text on ballistics. I'd appreciate any reference you could forward, if one exists. I have however seen it depicted as a random vibration pattern.

On the subject of "nodes" in the vibration whip;
The end of a cantilevered beam is always an "anti-node" for the multiple modes of vibration. Therefore the muzzle is always in a "whip" condition. A barrel has multiple nodes along it's length which you can actually experimentally demonstrate. I suspect you need help with the actual definition of a "node" in sinous wave patterns.

Please refer to my favorite quote from Art S.

Chris F is correct. I alluded to the fact in a previous post but didn't dwell on it. A node is actually a point at which there is theoretically no movement. A node cannot occur at an unrestrained end of a vibrating barrel. Release of the bullet at any node would be good thing. This could be studied experimentally by restraining both the reciever and the end of the barrel, with a sliding fit to allow longitudinal movement.
I too have never seen any mention of this type of figure 8 vibration. For that matter, I don't believe I have ever seen any circular vibration, which is what seems to be inferred in each half of the figure eight. Circular motion would not be vibratory in nature. I think what you are refering to is not the end describing a circle but the set map of the barrel end at maximum amplitude. This mapping would be caused by a combination of vibration and precession. Keep in mind that this set may not map continuously or evenly around the circle.

Chris,

What are your ideas on vibration nodes and modifying loads to them, I'm not sure but do you believe there are two main nodes on the vertical plane, with the barrel moving in a more eliptical pattern rather than a figure 8 of sorts, or something entirely different?

I'm not sure what pattern it whips in, but I tend to think it definatly has more vertical than horizontal deflection and does not make a whole lot of difference what shape it is really, after all the barrels dwell time will be longer at the most extreme point of deflection, still interesting to me none the less.

One thing Harold said in his book about muzzle expansion, he had measured barrel pressure at the muzzle with various loads using powders with different burning rates, I believe the psi was 6-12,000 psi is all. How much expansion that actually equates to I would be the last to know, whold depend upon muzzle dia and bore size though. Muzzle blast effecting group size was an interesting chapter too.

I hoped to give you a little teaser with the excerpt from his book, looked like it worked. Seriously, it contains way more than I could ever begin to tell. It is easy to read and hard to put down. Lots and lots of tests with good data, some inconclusive and others alot more. If this is something you like to read about, it's right up your alley. I'm sure Dan will love it. It's way more conclusive and specific than most anything you read about anywhere else, except maybe Precision Shooting Magazine which has good stuff in it alot of times.

Nice to hear everyones take on this.

Art, you posted right before me. I understand the barrel is still likely moving horizontally at the point of maximum deflection and may never really stop, although it does stop moving vertically momentarily, it's just relatively slower moving and more consistant (hence the Sweet Spot) and dwells in the "area" longer, you think that is a fair statement? I think that is all that is ever meant when anyone refers to a node, maybe more correctly called a lobe.

Brent,

If I remember correctly, Chris has the Vaughn book... He's mentioned it here before.

I'm surprised that I seem to be the only one here who has seen the depiction of the typical muzzle's path during barrel vibration. I guess I'll need to poke around and find a reference or two to that. The last reference I recall was in Rifleshooter magazine, but I can't remember even close to what issue. (And likely, someone would impugn that source anyway )...

This exchange has played out much like a philosophical debate. We're debating uncertainties, and I would put Chris and Art in the Socrates camp (That's a compliment, guys, okay? )... Socrates claimed "We don't know the truth, so sitting around speculating about it is a waste of time... I (Socrates) place myself above the speculators, since I'm aware that the truth is not and likely will not be known." Or something like that...

Other philosophers do take a stab at things, based yes on what appears to correlate with real world experiences. Often these speculations are wrong, and often they are right.
When enough men decided that the world was round and not flat, someone set about to see. But the funny thing is that even long after the earth had been circumnavigated several times, there were still those who would not believe it...

Dan

For those of you that do not know what a Rail Gun is go to this link:
http://www.benchrest.com/magnummetal/

Green788,
My thoughts would be more accurately summarized as;

quote:

---

Others much more capable than I have worked out much of the truth. I will seek these works out no matter how challenging and obscure and avoid concocting my own "pseudo-scientific" explainations (which is often the easier path).

---

I regret that I'll be off to Phoenix for a meeting for the rest of the week and will likely be off-line. I'll look forward to seeing the posts when I get home.

[ 03-06-2003, 10:35: Message edited by: Chris F ]

Chris,

These "others more capable than you" often disagree more vehemently than we do! For just about any study you can name, there will be a detractor claiming "inconclusive, improperly conducted, biased," etc...

Let's hope we can agree on at least these points:

1. Barrels vibrate during firing.

2. The muzzle's pattern during this vibration
will not be random, but rather will repeat
from shot to shot, provided these shots
exhibit the same impulse to the barrel.

3. It is better for the bullets to exit the
muzzle when the muzzle is nearly
stationary. (I say "nearly" because that's
as close as it's going to get).

4. The pattern followed by the muzzle will
depend on several things, among them the
barrel construction, bedding, and bullet
weight and velocity.

5. We can't agree on what this pattern looks
like, but we do know it is there!

Any dissenters?

Hopefully not... And so, if we do all concede these points, then all we are debating is the shape of the pattern followed by the muzzle. I've advanced my own thoughts on the matter, and a few others have advanced theirs. I've seen the notion I advanced in presumed factual accounts in the past. I'm sorry I don't recall exactly where. (I also recall learning the order of the first nine planets, and how to reduce fractions, but I can't remember the books that those revelations came from either )...

But basically, we really aren't arguing about much other than the shape of the vibration pattern. We agree it is there, we agree it is important, we just don't agree on how it typically looks.

Two out of three ain't bad...

Have a safe trip, Chris, and take care,

Dan

Regarding muzzle whip:

Has anyone just sat down at 200-300 yards and shot a couple of dozen same-load shots at one target and seen if it scribed a figure 8? or an ellipse? an oval? a circle? or something else? This would be the range of variation for one load.

How about changing seating depths and doing the same thing? should maybe scribe the perimeter of the shape of the barrel harmonic. THis would be the range of variation of one cycle of the whip (or lips, if the smoke ring theory held).

How about 0.1 graim increments of powder charges, all at the same seating depths? Perhpas this would scribe up and down, (or around) the full cycle of the barrel end whip.

ANd if the patterns were full of holes, like a shotgun group, then what we have is random placement within the pattern, and the smoke ring theory may be appicable as well!!

And if we have more of a perimeter pattern, with shots aggregated along the edges, then we have more of whip or swinging front barrel end.

And iff we have a perfect figure eight on its side, thenn we have an infinity sign, which is the amount of fun we can continue to have hand loading!!!

I gladly admit my ignorance in not knowing who has already done these simple tests. I also admit that here in Phoenix, we dont get enough still air to do that very easily, as wind would blow us out too easily.

You long range shooters, that put ten shot groups togetherall the time: are there patterns discernible?

...and let's not forget that different barrels might have different vibrational patterns. One barrel might be elliptical (bad), whereas another barrel might be figure-8 (better).

Pertinax

Jameister,

I've thought the same thing in the past, but the main hurdle there is the fact that as the charge weight increases, the recoil increases, so the muzzle whip pattern (whatever it looks like ) is retraced a little higher with each charge graduation. It doesn't stay in place.

The seating depth variations are more likely to show you the effects of the barrel's vibration whip at the muzzle. Check out BLR7's thread, and associated targets: http://www.serveroptions.com/ubb/ultimatebb.php?ubb=get_topic;f=6;t=007488#000000

You can see the effect on POI with very slight depth changes (keep in mind, though, that this is a 26" sporter weight, free floated barrel--IIRC).

Anyway, as bullet depth changes, pressure does too--which entails recoil changes, and you end up with another phantom, moving trace pattern of the vibration whip, if you see what I mean.

But for short strings in which the pressure and recoil are pretty even, the seating depth adjustments do seem to point to different parts of the muzzle's whip.

Dan

With great respect and all credit to Varmint Al, and his helpful web page, I end this thread with a thanks to all contributors.

I yield to the better science and the fantastic three dimensioal figures and movies provided by Varmint AL at hte link shown

http://www.varmintal.com/aflut.htm
http://24.124.39.10/uploads/modes.zip
A quote from one of these pages::

Full 3-D Finite Element Analysis of a barrel's first few vibration mode shapes and frequencies with LS-DYNA.

This is a 1.25" diameter stainless steel barrel 22" long with the far end fixed and you are looking at the muzzle end and it is tilted down slightly for better viewing. These are the first 9 mode shapes and frequencies. The frequency displayed is in radians/sec. To convert to cycles/second or Hz, divide by 2*Pi. Each bending mode (like movie1) is on one plane, but there was another identical mode in another plane at the same frequency that was not shown to save space. The torsional modes are at a high frequency. Note, modes 1, 2, 3, 6, 7, and 9 are shown in a single plane, but can exist in multiple planes simultaneously. Modes below a frequency of about 500 Hz will not be able to complete one full cycle before the bullet exits the barrel.

Mode Number Frequency
(rad/sec) Frequency
(Hz) Mode Description
1 455.11 72.43 Cantilever Bending
2 2819.4 448.7 1 Node Bending
3 7766.5 1236 2 Node Bending
4 8747 1392 Torsion
5 14348 2284 Axial Extension
6 14888 2369 3 Node Bending
7 23964 3814 4 Node Bending
8 26197 4169 1 Node Torsion
9 34719 5526 5 Node Bending

What this means to me explains the double figure 8 theory has a plausible explanation. there can be two simultaneous vibrations, a greater one cycling through a complet up and down and slightly elliptical around before the bullet leaves the barrel at about 400-500 Hz.

And a simultaneous secondary vibration cycle at about two to three times that frequency. VOILA we have an ellipse with a snowman, inifnity, double figure 8, or actually two small circles or ellipses, within the larger ellipse. of parts of two, or even parts of three...

Anyway the picture is clear to me how this can happen, and it is not from a radial expansion of the barrel, although that may account for the secondary cycles in a smaller orbit.

I am closing this thread, and copying this to another thread started called the figure 8 of the barrel whip as explained by fine pictures by Varmint Al, and as interpreted by smoke ring theory.