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Topic: Case capacity measurement, could this work? (Read 175 times) previous topic - next topic

Case capacity measurement, could this work?

It's close enough to the end of the month, I figure I can squander my monthly dumb idea allotment with this one  :D

From my audio days, I came to understand resonance, in particular the resonant frequency of air in a vessel.

The resonant frequency of air in both open-ended, and one-end-closed tubes is quite well understood. It's why wind instruments make sounds that gifted musicians turn into music.

There are factors other than the volume of air in the tube that directly affect the resonant frequency, but, I think, the volume of air is the biggest contributor, especially for vessels of very similar shape, proportions and material construction.

Instruments that measure audio frequencies very precisely are not over-the-top expensive.

I'm probably just whistling in the wind  :))  but, could the resonant frequency of the air in a brass case be directly proportional to the volume of air inside it? If so, can the resonant frequency be readily excited? If so, can we measure the frequency with a great deal of precision?  :-\

Alright then, back to my cave  O:)
Chris,
Retiring end of Q1-2021 :)

Re: Case capacity measurement, could this work?

Reply #1
The vessel itself is going to resonate itself with the frequency induced by the air flow. Would variance in wall thickness affect the recorded final resonance?

Re: Case capacity measurement, could this work?

Reply #2
Does the shape as well as the volume affect the resonance with a set constant air flow?

Re: Case capacity measurement, could this work?

Reply #3
What about air density/% humidity of the air used?

Re: Case capacity measurement, could this work?

Reply #4
This is beyond my pay grade.  :o
I can understand what your saying, I don't want to hurt my brain that much.

Re: Case capacity measurement, could this work?

Reply #5
😂 I know!

I’ve been trying to design (in my head) a machine that would do this for the last five years.

Re: Case capacity measurement, could this work?

Reply #6
All good questions Jerry.

The vessel itself will have a resonant frequency but it's likely to be quite different than that of the air mass, and perhaps less likely to be excited by the stimulus. Maybe. Also, it's easy to change the resonant frequency of the case by simply grasping it with sorbothane-lined jaws, or some damping material like that.

Shape does affect the resonant frequency. For example, if we found two different caliber cases that just happened to have the same nominal case capacities, one being a short action rifle, the other a pistol magnum, I'm pretty sure they would sound different. The question then becomes "who's the 600lb gorilla in the room?", Does air volume swamp minute shape differences?

As far as air density and humidity go, I don't know if that matters. Does C on a flute sound different in Denver versus Seattle?

The other thing unknown to me is the Q-factor of any measurable resonant frequency in a tube as small as a cartridge case.

Quote
The Q, or quality, factor of a resonant circuit is a measure of the “goodness” or quality of a resonant circuit. A higher value for this figure of merit corresponds to a more narrow bandwidth, which is desirable in many applications.

Fun stuff to think about.
Chris,
Retiring end of Q1-2021 :)

Re: Case capacity measurement, could this work?

Reply #7
Would a change in volume of air flow per Sec change the frequency?

Re: Case capacity measurement, could this work?

Reply #8
Would a change in volume of air flow per Sec change the frequency?

I'm not sure, maybe we have some wind instrument musicians on here who could address that. I would think a small DC fan would provide a constant airflow across the case mouth.

Just for the record, my talent as a musician can fit in a small rifle primer cup, but I recall when I was forced to come to terms with that deficiency in high school, more air resulted in more loudness, not a change in pitch. 
Chris,
Retiring end of Q1-2021 :)

Re: Case capacity measurement, could this work?

Reply #9
 :-*
Dave

Re: Case capacity measurement, could this work?

Reply #10
WTF ????   Has the cold weather frozen ya'lls brain cells or is this some alien language mis-directed to this site?
 
 I don't live in Texas, so I can use water to measure case volume any time I want ! 

LOL!

Re: Case capacity measurement, could this work?

Reply #11
WTF ????   Has the cold weather frozen ya'lls brain cells or is this some alien language mis-directed to this site?
 
 I don't live in Texas, so I can use water to measure case volume any time I want ! 

LOL!

😂
Yep! Me too but it’s tedious.

Re: Case capacity measurement, could this work?

Reply #12
Just shoot it!!
Theoretically if case volume is lower than standard higher preasure and poi.
If case volume is higher than standard, lower preasure and poi.
All can be confirmed with a chronograph.
Or did I miss something?

 

Re: Case capacity measurement, could this work?

Reply #13
@ BCz - Well ya maybe. 😂

You just described controllable vertical in your group. Theoretically you can select away from it via case sorting. The age old question is : whether or not sorting simply by weight is adequate to attain that goal.
As I do more of this type investigation, the more I’m feeling that the need to sort may actually be most dependent on what brass manufacturer you are using.

Re: Case capacity measurement, could this work?

Reply #14
Just shoot it!!
Theoretically if case volume is lower than standard higher preasure and poi.
If case volume is higher than standard, lower preasure and poi.
All can be confirmed with a chronograph.
Or did I miss something?

True enough until you deal with barrel time and whip....
Dave