Adjusting a Tuner using sound

[MKnarr]

Jim Pollard and I have been looking at the possibility of adjusting a tuner using the sound waves caused by firing a round. This technique could be a time and money saver if it worked. The thought was, if there was a way to get the vibration patterns into a computer, we might be able to tell if the tuner was adjusted correctly or not.

Here is a web site where you can see the results. Tuner adjustment using sound


Unfortunately it hasn't worked out so far but the actual vibration patterns caused by the barrel ringing as the round is fired are interesting anyway. Many of us worry about barrel vibrations but few realize that the vibrations that are important occur in less than .003 seconds (the time it takes for the bullet to leave the barrel) for a 22LR and looking at the waveforms we recorded, there isn't a lot going on in that short a time.

Here is a barrel vibration wave that Jim sent to me today.

It appears to be exactly what I would suspect that vibration pattern of a ringing barrel would be when firing a round. It is about .15 seconds long but the only part we are interested in is the first .003 seconds.

There was a question and a lot of speculation on another forum about how long a barrel vibrates after the shot is fired. In our testing it appears to around 1/2 second or less depending on the barrel diameter, shape and length and attachment to the receiver, at least as close as we can measure.

Take a look. It isn't anything earth shattering but it might add just one more piece to the puzzle and we would be interested if anyone had any better thoughts.

Jim B.

 

[Jerry H]

I would think a combination of sensors would be needed to "see" what is really happening. Strain gauges at the chamber and muzzle for timing and solid state accelerometers at the muzzel in at least the verticle axis for the movement pattern.

 

[MKnarr]

How many shooters have those things laying around at home?

 

[alan k]

Bob Collins once told me a well tuned rifle has a dif sound. I can't tell. Bob, if you read this thread please add comment.

Al Kunard

 

[Kent Owens]

Will Hickman did a lot of tests on this several years ago. He went by WillH on the forum. One thing I found interesting from his tests was that the vibration ws the virtually the same when you dropped the firing pin on a fired case. The lines on the graph were just accentuated, but the same pattern. You may do a search for posts by WillH. He was an electrical engineer, I believe, and had the means and necessary tools to do such testing.

 

[Boyd Allen]

I know an accomplished RF shooter that has one of those ugly Sims rubber doughnuts somewhere in the middle of his barrels. Evidently they do something that is helpful to accuracy. Of course there are other types of mid barrel tuners. I would like to see a sound trace of a rimfire barrel with one of The Sims devices in place. My casual testing on a mounted CF barrel gives a striking difference in the sound when tapped, going from ringing to a thud.

 

[Jim Pollard]

Kent
I tried the search you suggested and no usable results. The link listed has some tapping results to find the node on a barrel.

alan k
I too would like to hear what Bob Collins might have to say. He wrote some things about listening to the barrel, a while back.

 

[Kent Owens]

Jim,
Will may have deleted all the stuff that he wrote. It was new territory and if I recall his data wasn't received well. Will didn't suffer fools well, so I guess that's what happened to it
Then again, the site has been down several times since 2005-2006 and it may have been deleted/erased.

Anyway, what I gleaned from it was that different action designs produce different vibration signatures that need to be dealt with, and I think he was onto something there.
Different firing pin weights and different springs make a difference.
Will has since stopped shooting and began building an operating model steam engines, or ttat's what he was doing the last time I talked with him.
I'll do a search and se eif I can scrape something up.

 

[Pete Wass]

Barrel Time:

It would seem to me that what the barrel does after the bullet has exited makes no difference to accuracy. It's what goes on while the bullet is in the barrel that matters, no? If this be true then the amount of vibration to be studied is quite small in terms of a graph, no?

 

[MKnarr]

I agree Pete. According to Varmint Al's calculations the bullet will leave a barrel around .003 seconds more or less. That why we are interested in that area. In the web site I listed, I mentioned several times that the vibrations, even though there are a lot of them, don't mean much in terms of accuracy after the bullet has left the barrel.

 

[Jim Pollard]

Pete
Jim and I kinda pushed each other on this and Jim B did the computer work. if you look at the wave form above, the trigger has released the firing pin, firing pin has struck the shell, fired and bullet has exited the barrel all within about the first .003 of a second as I understand the real world. that is about the first one forth of an inch on the wave. If I am wrong tell me why and where , this is a learning process for me also. I am not an engineer.
Jim P

 

[Jim Pollard]

Hi Jim
I pushed post and you beat me to it.
Jim

 

[Boyd Allen]

If there were a line on the graph that showed then the trigger was pulled, how would you go about determining its location using the data?

Out of curiosity, I looked up the speed of sound in various materials.
http://www.piano-tuners.org/sound.html
It would seem that the noise of various events that occur prior to the bullet's exiting would get to the muzzle considerably faster than the bullet, and may have cycled several times prior to that event. Perhaps this might lend credence to the thought that damping is an issue.

 

[MKnarr]

Boyd, here is our thinking. Here is a picture of the vibrations created when the trigger is pulled and the firing pin hits an already fired case.

From the time the trigger is pulled to when I believe it hits the case is about .001 seconds.

Here are two pictures of fired rounds with 8 and 10 ounces of weight on the tuner.

The only significant difference I see is the amplitude of the two peaks circled in blue. Assuming that Varmint Al's calculation that the bullet leaves the barrel in about .003 seconds and if I subtract .001 for the lock time from the position of the left peak, it would seem to me that this is the point when the bullet exits the barrel rather than one of the other peaks.

Suppose for a minute that it is, I don't know if it is telling us anything anyway. I've speculated with Jim P. that the difference in amplitude could simply be a function of velocity (or pressure) and doesn't mean anything to the effect of the tuner.

It's been suggested several time that attaching something to the barrel would be better. I don't know about that. I think that if anything is attached to the barrel, you won't get true readings because the instrument should affect the vibrations. If it didn't, a tuner shouldn't work.

The truth is after many hours staring at these pictures, I don't know that this is going anywhere without someone smarter than me. By posting what we have tried, we're hoping that some one else might have a better idea.

 

[Vibe]

MKnarr
Is that a plot of sound amplitude? If so the highest amplitude of that plot will be occurring when the barrel is moving the fastest and generating the largest pressure wave, in the air or in the steel - which is not when you want the bullet to exit. I do not see where you might have converted decibels to position as the two plots will not be identical - more likely the inverse of each other. Also I'm thinking I went through the calculations before and found that he bullet exits around 0.0027 seconds after primer ignition as opposed to 0.003 from firing pin release. You may very well be onto something though - I'd thought of drilling very small divots into a barrel and setting a phonograph needle into it - but the overall gross recoil would need to be contained pretty tightly in order to not destroy the device with each shot. But again that would really only measure barrel movement velocity, and not position.

 

[mks]

Suppose for a minute that it is, I don't know if it is telling us anything anyway. I've speculated with Jim P. that the difference in amplitude could simply be a function of velocity (or pressure) and doesn't mean anything to the effect of the tuner.

It's been suggested several time that attaching something to the barrel would be better. I don't know about that. I think that if anything is attached to the barrel, you won't get true readings because the instrument should affect the vibrations. If it didn't, a tuner shouldn't work.

The truth is after many hours staring at these pictures, I don't know that this is going anywhere without someone smarter than me. By posting what we have tried, we're hoping that some one else might have a better idea.

Jim and Jim,
You could be on to something here. Then again, maybe not. The trouble is that you aren't measuring what really matters, which is the slope of the muzzle when the bullet exits. Sound pressure is a measure of acceleration of air, which is caused (hopefully, if one does it right) by the acceleration of the barrel. To calculate muzzle slope, you would need to integrate the muzzle acceleration twice (one integration yields velocity, the second yields position), and you would need signals from two different spots near the muzzle, say 1" apart, to calculate slope. Such calculations are fraught with inaccuracies that may make this method impractical.

However, if some characteristic of the simple sound pressure measurement empirically correlates with tune, then who cares why as long as it works? There are plenty of examples of scientific research that use this approach. (One set of investigators finds a correlation, and others work for years trying to figure out why.)

Fun stuff,
Keith

PS. We have glued an accelerometer to the muzzle of a rifle, and came to the conclusion we need a way of directly measuring muzzle position. There are some candidate methods that look interesting, for instance, inductance and capacitance. Commercial laser sensors look too expensive, but one could in principle rig up a cheaper one.

 

[Jim Pollard]

This was not an expensive thing to try. The programs can be downloaded free and the head from the stethoscope for about $ 10.00 and an old mic from an old tape recorder.
I can change the wave patterns with some controls in the computer but Jim B was the man that put it together from my idea. I have no idea what I may try at this time. Any thing attached to the barrel could change the tune on the gun, I think.
just thinking out loud.
Jim P

 

[mks]

This was not an expensive thing to try. The programs can be downloaded free and the head from the stethoscope for about $ 10.00 and an old mic from an old tape recorder.
I can change the wave patterns with some controls in the computer but Jim B was the man that put it together from my idea. I have no idea what I may try at this time. Any thing attached to the barrel could change the tune on the gun, I think.
just thinking out loud.
Jim P

I would be interesting to see how the signal changes depending on where you place the stethoscope. If you get repeatable differences between two locations, say 0.25" back from the muzzle and 1.25" back from the muzzle, then that would be promising. Then it might be worth recording the two signals simultaneously and attempting the calculation of muzzle slope.

Cheers,
Keith

 

[Jim Pollard]

Keith
The stethoscope head is attached to the stock, under the action area with tape. That way it would not have any influence on the barrel its self. I am not an engineer, just common sense ( shop teacher) but any thing attached to the barrel would result in false readings. Is that wrong?
Jim

 

[Varmint Al]

Boyd, here is our thinking. Here is a picture of the vibrations created when the trigger is pulled and the firing pin hits an already fired case.

From the time the trigger is pulled to when I believe it hits the case is about .001 seconds.

Here are two pictures of fired rounds with 8 and 10 ounces of weight on the tuner.

I am not sure what is actually being measured, but... Looking at the first 0.003 seconds of the curve looks very similar to the FEA calculations of the muzzle projection curve for Esten's 22LR rifle with the reverse taper and no tuner. The timing is remarkably similar.
Good Hunting... from Varmint Al