Vibration analysis

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Last Post 29 October 2008

Standard Member

TRKakaCatWhisperer posted this 26 October 2008

I'm looking for the basic research that's been done on the nature of the vibration of a rifle barrel and the effects on accuracy.

Dr. Franklin Mann published some observations back in the 1920's defining the position of the barrel at the moment of bullet exit and how that would affect bullet point of impact.

Devices to control it include the Boss and the rubber donut thing. Each with it's own method of 'control'.

Some folks have hung wires/coat-hangers on the barrel to determine nodes of vibration (when the barrel is thumped - watching which ones vibrate which ones don't).

Some match rifles are free-floated.

Some have adjustable points of contact at the end of the forestock (Win 52D for example).

Many rifles are noted for being finicky as to forend pressures (Ruger #1, Handi-Rifles).

SO, what's out there that folks have published or researched? Where's JoeB ?

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CBA Member

RicinYakima posted this 26 October 2008

You may wish to research Rifle Accuracy Facts by Harold R. Vaughn, Sandia National Lab, published by Precision Shooting, Inc., 1998. Ric

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Standard Member

TRKakaCatWhisperer posted this 26 October 2008

Cool, THANKS!

Anything where someone has acturally used an accelerometer to measure the vibration?

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CBA Member

RicinYakima posted this 26 October 2008

I'm not a mechanical engineer, so some of it is way over my head. However, the section on barrel threads and action stiffness was very interesting. Ric

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Standard Member

Notlwonk posted this 26 October 2008

Precision Shooting magazine has had several articles on vibrations. One of their writers, a small bore riflesmith by the name of Bill Calfee, has done some interesting work on the subject. He uses a weight on the end of the barrel.

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CBA Member

codarnall posted this 26 October 2008

Rifle Accuracy Facts by Harold Vaughn has a nice treatment of vibrations with fully instrumented test bed setups.

-Charlie

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CBA Member

billwnr posted this 27 October 2008

Vibration analysis might be fine for those who don't have the time to shoot.

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Standard Member

TRKakaCatWhisperer posted this 27 October 2008

billwnr wrote: Vibration analysis might be fine for those who don't have the time to shoot. Might be. For me I can't afford to shoot using a rifle that has an issue with vibration that can be easily be fixed.

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CBA Member

billwnr posted this 27 October 2008

There's two ways to “tune” for shooting. One involves adjusting the primer/powder/bullet/bullet seating depth until desired accuracy is achieved.

The other involves a “tuner” screwed on the end of a barrel. The “tuner" is what is adjusted (screwed backwards/forwards ), not the load.

I can see where a tuner would work for jacketed bullets or even swaged factory load .22 rimfire bullets but... think it would be a little unwieldy in CBA cast bullet shooting.

If a cast bullet flies out of the group at 200 yards how does one figure out what cause it? Is it 1) defective bullet, 2) mis-read wind, 3) unbalanced/untuned load or 4) poor “follow thru"?

Also I think the addition of a metal tuner would disqualify a Production class rifle.

I think a person who can read wind flags good could shoot better groups with an average load than a shooter who can't read wind could using a more accurate rifle/load.

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Standard Member

TRKakaCatWhisperer posted this 27 October 2008

I'm in close agreement with you. But what I'm looking at is not the tuning (as you noted the 'devices' are likely not leagal in competition. My concern is the determination of how much (and what effect the vibration has) and to control it, hence controlling ONE more factor in the many things that affect group size.

If one can measure (or measure the effect of) vibration then one has the abiltiy to control the effect.

Mann did some experiments with orientation of bullets - closing down the group size not by controlling the out of round/ballance bullet but using the knowledge of where it was out and orienting in the same direction - net effect: smaller group.

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CBA Member

billwnr posted this 27 October 2008

TRK wrote:

We do this part with “bump” dies. It's lots easier than messing around with bullet orientation.

Feel free to install a “tuner” on the end of your rifle. BENCHREST.com is where all of the tuner discussions are. If I were you I'd do my tuning tests with jacketed bullets. In my opinion trying to use a tuner with cast bullets would be like trying to do testing the hardest way possible.

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Standard Member

CB posted this 27 October 2008

Tim,

Just my .002 on the issue of barrel vibration but I think it should be one of the last things to worry about in our game. Now with a 22, shooting factory ammo, or once you have your rifle shooting like the jacketed BR guys there seems to be something to it but when reloading and dealing with cast bullets where you can tune the load and have so many other variables to contend with barrel vibration is pretty far down on my list. I noticed on the Browning site that there's not much about the Boss anymore and I think only one rifle has it and they don't show a photo.

Not to say it isn't a interesting subject and something to toss around the campfire but I don't think it'll turn a run of the mill cast bullet load in to a tack driver and you'd be much better off working up a good load and sticking a couple of flags out in front like Bill suggested.

To answer your original question though I don't know anything about vibration analysis so obviously don't know of any research.

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Standard Member

TRKakaCatWhisperer posted this 27 October 2008

Pat - in general I agree with the set of priorities you've set out, but for the fact that I'm working with a Handi-rifle. It has a sensitivity to vibration, fit of barrel to frame and fit and mounting of forend to the barrel. That is the reason for my persuit of measuring the vibration - to get the groups to reasonable size - jacketed as well as cast. But since cast bullets are what I am persuing (to get to a 1” group at 100yds) with the handi rifle (and a few other single shots) it's a challange. Most folks are satisfied with trying the traditional things; I want to understand the mechanisms following the event of ignition and of internal ballistics.

Yes, benchrest central is a wealth of information. The handi rifle is hardly in their relm of credibility; and cast bullets are not used by many of the folks using the handi-rifle forum on GBO (hunting accuracy is very good for those folks).

So the mere topic is a red-haired step-child on any of the boards.

But HERE we have a TOPIC relating to ACCURACY and the answers given have been useful in collecting in one place a broad range of related information relating vibration and accuracy.

THANKS!

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Standard Member

CB posted this 28 October 2008

I don't have one but I can't think of a worse design than the Handi Rifle to use to try to isolate barrel whip alone as a cause of inaccuracy considering the potential for the whole assembly to shimmy around when it's fired. I think it's pretty amazing they shoot as well as they do considering their design and some of the cartridges they're chambered for.

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CBA Member

codarnall posted this 28 October 2008

<*>Vaughn's book,is more than you wanted to know I'm sure. When I said instrumented that's what I meant... strain gauges etc. Get the book! Hal's been gone about 10 years but this is about a life's work from serious test engineers.Charlie

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Standard Member

TRKakaCatWhisperer posted this 28 October 2008

Charlie - I will! I have a laptop issued by my boss and I do LabVIEW programming for a living. My intent is to DO some instrumentation and take the rifles to the range.

Pat - again we agree. There are things that folks do, like ensuring equal clearances on either side between barrel face and frame face, continuous and even contact between mating parts of the latchup mechanism and others.

Looking to see what others do is a starting point. One of my objectives is to end up with a low-dollar rifle that with a little tuning will do 1” at 100yds with plain base cast bullets. Of course what I learn will be applied to every other rifle I own.

It's the drive to find out WHY.

THANKS!

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Standard Member

CB posted this 28 October 2008

TRK wrote: It's the drive to find out WHY. Have to agree with you there and hope you post your findings.

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Standard Member

CB posted this 28 October 2008

Tim It appears we share some common skills. In my former life among the working, I worked for Tenneco Automotive in the NVH lab as a Sr. Lab Techie and did Labview work and instrumentation. I was fortunate to have Megadac recorder with lots of channels.

What do you plan to instrument with? Accelerometers, strain gauges? I hear there is a kit available that has a series of strain gauges and a program for a laptop, but dont know who makes it.. I think it most likely isnt very high quality, strain gauges must be applied by someone that knows how to do it...

I think if you are looking at vibration, accelerometers would be the way to go, but combining with 3 rosette gauges may yeild more useful data.

I have often thought about using some pressure sensors combined with the above, but these things are not cheap and not affordable on a fixed retirement income.

There are days I wish I still had access to the lab... Ah those were the days.

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CBA Member

billwnr posted this 28 October 2008

one thing that would really help would be to get a new throating reamer and make the throat of the handi-rifle match up to the bullet you want to shoot.

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Standard Member

TRKakaCatWhisperer posted this 28 October 2008

billwnr wrote: one thing that would really help would be to get a new throating reamer and make the throat of the handi-rifle match up to the bullet you want to shoot.

I agree. There is a marked difference between the .44Mag 1-38 and the .444 1-20.

Don't know yet which is better, but hand seating 260gr Lyman's is much smoother with the .44Mag BBL.

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Standard Member

TRKakaCatWhisperer posted this 28 October 2008

Jeff -

I use LabVIEW to do final testing of the DC Brushless motors we make. RPM, current, starting conditions, torque, %duty cycle and quadrature on data and commutation tracks, variation of speed within each revolution, missing pulses and much more.

Vibration analysis on some motors and spectral analysis of sounds of others.

Yes, I'm looking at a Dytran triaxial accelerometer - all three in one device. First job is to start small with a .22 to get the right range of response.

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Standard Member

CB posted this 28 October 2008

Dytran makes good accelerometers. 3 planes is a good choice. Are ya gonna borrow one from work or are you footin the bill on this?

It will be interesting to see the difference between difference calibers like 22, 6mm and 30.

I bet you could find a lifelong amount of work in just testing this with all of the variables, barrel type and length, load, bullets and environmental effects... I can imagine what the test plan for that would look like!

Now if you can figure out a way to earn a living doing it, god I would be in heaven!

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Standard Member

TRKakaCatWhisperer posted this 28 October 2008

Having just looked up the prices on the accelerometers, the single axis is over 300 and the tri is over 900. I think I'll use this exercise as a learning-exercise for the applications at work.

Thanks, Jeff, for your comments on the brand. I've used a few around the plant, but never had to purchase any. LabVIEW has a USB interface device for only 160 bucks that will be my first choice - it's limited to 20kHz but that may not be an issue.

As I understand it most of the vibration is vertical as opposed to side-to-side and I'm sure there's some stiff axial movement as well.

At the speed things move it's likely that I'll get this rolling by spring - nothing moves fast unless the boss dictates it.

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CBA Member

codarnall posted this 29 October 2008

I spoke to a friend about instrumentation as I recently helped him integrate his steady state analyzer to his notebook. I was thinking that such a tool with a fourier analytical mode could help to do a backwards vibrational mode analysis. He quickly indicated the microphone limitations etc. It would seem to me that the step or impulse response is what your looking for in first order responses. Light weight piezio devices seems still to be the order of testing. That said, even with new tools the whole subject has already been solved in art form by gun witchdoctors. It would be interesting to see if new test instruments would help in the first order analysis. Guru's on this forum and others have already “tuned” their artillary with tried and true techniques, again an art.

Charlie

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Standard Member

TRKakaCatWhisperer posted this 29 October 2008

Charlie - good point on first order vibrations. That is of course the resonant frequency of the barrel itself. But there are other events that the accelerometer will pick up. Reducing the vibration is the goal. Tuners will move the node (least vibrating point) fore and aft. Other devices will dampen the vibrations. With some rifles there will be odities that help or hurt. Notably with Handi-Rifles the forearm and the lockup mechanism. One fellow is ensuring that the clearance between the barrel and frame at the breech is exactly equal and not greater on one side. I expect to be able to document differences of each variable.

Someone on benchrest central noted the double pressure spike. The first from ignition an the second from a bullet seated well off the lands when it contacted the lands. This too should be observable.

I don't have a chrono, but I have watched Bill Alexander (Alexander Arms - Beowolf) use strain gages and a chrono to relate pressure to velocity in load development.

I want to correlate accuracy and vibration. Is there SOMETHING observable about that *&%(& flyer? If so, can it be tracked down?

(fourier transforms are available in LabVIEW to transform time domain events to frequency domain - to identify the frequencies present in the noises/vibrations recorded. From there one looks to find the resonant element - small things resonate at high frequency (like balls in ball bearings) and large things at lower frequencies - like frames and barrels. Then the issue one of control.)

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CB posted this 29 October 2008

I wonder if a grant could be secured to offset the initial cost of the sensors and a legal copy of LabView???

Let me look into this, they give grants all of the time for all kinds of stuff like this.

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Standard Member

TRKakaCatWhisperer posted this 29 October 2008

If one qualifies, there are 'student' editions that are available at quite reasonable rates.

Too bad I'm no longer a professor.

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CBA Member

JetMech posted this 29 October 2008

It amazed me when I started BPCR shooting that the shooters support the forward end of the rifle directly on the barrel. This goes against everything I had learned about bench shooting. After some research, I used the basic procedure of sprinkling talcum powder the length of the barrel, shooting a round supporting the front of the rifle on the action, and seeing where the talc remained. It clearly showed the neutral points as far as barrel vibration. Using those points (trying 3 different ones) showed that accuracy was improved by suporting my barrel about 6 inches from the muzzle over what I got supporting the rifle on the action or forend. Granted, my Browning has a 2 piece stock, so this method may not be applicable to bolt rifles that are free-floated or competantly bedded. But then, using the neutral point may ensure you are not changing the vibration pattern, but are dampenning total vibration without adding anything to the rifle. Not very scientific and I have not conducted any experiments on my 1903. Just somethging to think about. Has anyone done testing on bolt rifles using this method?

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Standard Member

TRKakaCatWhisperer posted this 29 October 2008

But the technique of supporting the end of the barrel is often done with a 'sled' which adds MASS to the end of the barrel which 'tunes' it or at least dampens the vibration.

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CBA Member

JetMech posted this 29 October 2008

That's true in bench rest work. I don't know that any attention is paid to finding the neutral point. In BPRC for sillouette or long range work, we use cross sticks. In my case, a leather sling supports the barrel at the neutral point. No added mass there.

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CBA Member

codarnall posted this 29 October 2008

You mean the talcum powder business actually worked. I about beat my vise to pieces trying to find nodes on a worthless 240 WM years ago. The solution was to trade for a hand picked 257WM with Roy himself looking over my shoulder.

Charlie

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CBA Member

JetMech posted this 29 October 2008

Yes. I tried it for 5 shots and the talc collected / remained in the same spots. Not much but visible and consistant. There's some old timers who can hold the rifle under the action and hit the barrel at different points to find the “dead spot” as they call it. I tried with mine after identifying the points, but couldn't tell the difference.

Vibration analysis

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