Barrel Vibration testing

David Merrill said:
Some interesting reading for you.

http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA162135

http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA201713

http://www.arl.army.mil/arlreports/2000/ARL-MR-492.pdf

http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA474853

http://www-personal.umich.edu/~cwkauff/Aero729/file/PRODASV3 User.pdf

Note mentions of 'muzzle jump' and 'aerodynamic jump'.

David Merrill
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Excellent resources for this topic. In the Bornstein, et al. 1988 report, they measure tank cannon muzzle angle with eddy current proximity sensors. At least six are needed, three each at two points near the muzzle. These also provide horizontal and vertical displacement information. It is remarkable how closely their figure 6 (View attachment Cannon muzzle slope.pdf) of muzzle slope matches VarmintAl's simulation results.


There is a comparison of eddy current and capacitive sensors at http://www.lionprecision.com/products.html. In general, capacitive has higher resolution, but lower frequency response. Either could work well enough. Price is not listed.
 
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For almost 100 years, there was an idea about how bullets were blown by the wind that was universally accepted as fact. Documented in books, accepted by the Military, by ballisticians, etc. After further investigation, it was shown not to be fact. Now it is accepted that drag causes the effects.

With barrel vibrations, a whole lot of this is voodoo to most of us. Even those who've got a pretty good grasp on things are reluctant to just start blirting out answers. This is a little more complex than measuring the diameter of a bullet. What that means to most of us is that there's going to be fewer people working on finding the facts, and that there's going to be a good deal of disagreement on them once they're found. That doesn't mean people should not look. And it does not mean that a person has to account for all things in order for their findings to mean something.

The troubles with this particular research are several. It requires effort in several different fields to mean anything. It is not the sort of thing that sharing information is a big help, so, it does not lend itself well to cooperation. That's probably the biggest issue. Besides that, a person has to have a machine shop and be willing to delve into electronics a bit, not a common combination. Last but not least, we may be looking for a problem that doesn't exist. The real testing should be done by taking a 0 shooting gun, and making it worse.
 
The reason for so many of the questions I am asking especially concerning vibration other than vertical is the possibility of an elliptical tuner. I have an idea but before I go to the expense of trying it I want to know if there is anything to warrant it or is it all in my imagination.
I wish Jonathan could get video like he was talking about and that would solve a lot of it..

But then again if we really start finding out all of the secrets that really make a difference then the sport wont be so much fun just trying to figure it out.
 
Boyd Allen said:
If we imagine that a thing works a certain way, we only have a theory, until testing verifies it, and even if the result is an improvement in performance, there is a good chance that we may not totally understand the reason for the change, because in making the intended change, it is highly likely that we have changed something else, that we were not looking at. I love imagining how things work, with an eye on making them work better, but without the capability of building what we imagine, so that we can test as we go, all that we have is a pleasant, albeit harmless distraction. This is why my next goal is not a new rifle, but a lathe, so that I can build and test ideas....cut and try.
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Awesome! You are going to have some serious fun! You will soon wonder how you ever managed to get this far in life with out a lathe.

Fitch
 
Some, myself included, disagree with the verity of this statement "However, it is the pressures generated by the burning primer and powder that gives rise to the barrel vibrations."

I believe that a large portion of the overriding vertical component is generated by the use of a mechanical firing pin.

al
 
It's not the pin itself, it's the fact that the mechanism holding the pin back puts a vertical tension into the system.

I think this overriding vertical component is necessary for tuning, I've heard that electrically ignited systems, "stretchers" and even barrel blocked systems which often produce round groups through a wide velocity range can be nearly immune to "tuning" techniques.

For myself I've only played with blocking and bedding but I spend my life "making the rifle produce good clean vertical" and then "tuning it out." If I can't make a rifle produce vertical I'm lost.

round groups suck, unless they're dots.

Vaughn didn't get into this in 'Rifle Accuracy Facts'

unsupportedopinionsby





al
 
alinwa said:
Some, myself included, disagree with the verity of this statement "However, it is the pressures generated by the burning primer and powder that gives rise to the barrel vibrations."

I believe that a large portion of the overriding vertical component is generated by the use of a mechanical firing pin.

al
Click to expand...

Firing pin force is 20-25 lbs. Bolt thrust due to 60k psi peak chamber pressure on a .473" diameter case rim (0.176 square inches) is 10,500 lbs, over 400 times larger. I can't see how the small firing pin force can cause more vertical than the much larger powder burn force.

Although I don't agree with his calculation method, Vaughn on page 67 estimates the dispersion due to variation in firing pin force to be no more than 0.007-0.010" and concludes that "firing pin impact is not a significant contributor to dispersion."

If firing pin impact were the most important cause of vertical vibration, then one would expect a Remington Etronx rifle to have less muzzle jump on recoil. My 243 Etronx has as much muzzle jump as one would expect from a rifle with a mechanical firing mechanism. It also shoots groups that have about the same vertical as the average Rem 700.

Cheers,
Keith
 
mks said:
Firing pin force is 20-25 lbs. Bolt thrust due to 60k psi peak chamber pressure on a .473" diameter case rim (0.176 square inches) is 10,500 lbs, over 400 times larger. I can't see how the small firing pin force can cause more vertical than the much larger powder burn force.

Although I don't agree with his calculation method, Vaughn on page 67 estimates the dispersion due to variation in firing pin force to be no more than 0.007-0.010" and concludes that "firing pin impact is not a significant contributor to dispersion."

If firing pin impact were the most important cause of vertical vibration, then one would expect a Remington Etronx rifle to have less muzzle jump on recoil. My 243 Etronx has as much muzzle jump as one would expect from a rifle with a mechanical firing mechanism. It also shoots groups that have about the same vertical as the average Rem 700.

Cheers,
Keith
Click to expand...

keith,

It's not about relative force. It's not about firing pin impact. As I said, Harold didn't talk about it in the book.

Remington Etronix setups shoot round groups..... BIG round groups.

al
 
mks said:
Please explain.

Thanks,
Keith
Click to expand...

Due to the angled sear engagement surfaces forces, the cocked system is not only biased upward but actually bent. The situation has been recognized for years and system mods like 'Borden Bumps' and parallel engagement surfaces, bolt lug/boltface modifications and trigger timing address it.

The major vertical drivers associated with the firing impulse are barrel droop and assymetrical bending from recoil lug flexure. And its associated flexure of the stock...

I believe that eliminating or mitigating certain of these vertical components leads to an un-tunable system.

al
 
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