Guys who use the water method should be able to answer that (I've never sorted by volume - I could never bring myself to use that messy method). Logic suggests that once fire-formed and trimmed to length, heavier cases would have less internal volume, but I don't know if that bears out in testing for it.
Digital case volume meter
- Thread starter lrgoodger
- Start date
Someone posted on this website months ago a comparison of weighing and volume sorting. The two methods didn't line up.
There is some correlation, but it's not 100%.
I have tested this with 100 cases,,and would not trust weight to sort cases.
Looking at case volume from a real point of view, equal volumes is all that matters.
Measuring and then correcting case volume variations is the best place to start precision reloading. As I posted earlier, how to change case volume is the question now!! It's like checking your tire pressures and then not bothering to making them equal.
Where the bullet hits the target is then to do with the other variables of reloading and shooting.
LC
Measuring and then correcting case volume variations is the best place to start precision reloading. As I posted earlier, how to change case volume is the question now!! It's like checking your tire pressures and then not bothering to making them equal.
Where the bullet hits the target is then to do with the other variables of reloading and shooting.
LC
nice... i'm going to try that right now!
I read this thread and I wanted to see if I could sort cases via arduino with a bme280 sensor and a LCD screen and then to place that sensor inside a pressure vessel and try to draw a known volume of air from the equalized vessel with a fired case attached. Basically I tried to put a barometric sensor in a pressure vessel, simply a weather station arduino project. I found my 1st try was unsuccessful as the tubing I used to build the vessel was too soft and was deforming while pressurised, this made it difficult to obtain consistent readings. Some issues I noticed my fingers would heat the case when handled which would cause the recorded pressure to rise and add to the measuring error, also I noticed that the process became more difficult when a weather system was moving through the area as a falling barometer would cause the initial equalized value to shift so measuring the difference required noting the new room or equalized value.
Other observations the H2o capacity standard deviation on a few of my fired lapua .284 cases was around .005 ml and the extreme spread was .014 ml this difference should be measurable with the .10 hpa accuracy reported by the manufacturer on the data sheet. As my 1st pressure vessel was about 10.5ml with a 4.383 ml case attached and by increasing the volume to around 11ml the pressure a .10 hpa variance was equal to around .001 ml.
It should be noted Quickload shows these small differences in case volume do not affect muzzle velocity in a meaningful way for example a using my .284 case with a 183 sierra going from a coal of 3.329 to 3.328, a .001 inch seating depth reduction pushing the bullet further into the case is about a .002 ml of volume reduction of usable case capacity and results in about a .007% increase in peak pressure using 53.8 grains of rl 23 (w/ trued burn rate).
On paper the $5 sensor looks like it is precise enough but my observation so far haven't verified it yet due to my poor choice of material in constructing the pressure vessel. If you're interested in giving it a go the parts list is as follows which is about 40 bucks worth of stuff. Also if anyone has a better sensor suggestion I would be interested.
Arduino mega (or your favorite arduino style)
Bme280
3ml syringe
LCD shield or display of your choice
Some 8mm tubing and fittings I recommend hard plastic tubing or a vessel that will resist expansion or collapse under pressure or in a slight vacuum if you're increasing the volume of the vessel.
Links for weather stations build guides with sketches to run the sensor on the arduino.
https://learn.adafruit.com/adafruit...sure-temperature-sensor-breakout/arduino-test
Other observations the H2o capacity standard deviation on a few of my fired lapua .284 cases was around .005 ml and the extreme spread was .014 ml this difference should be measurable with the .10 hpa accuracy reported by the manufacturer on the data sheet. As my 1st pressure vessel was about 10.5ml with a 4.383 ml case attached and by increasing the volume to around 11ml the pressure a .10 hpa variance was equal to around .001 ml.
It should be noted Quickload shows these small differences in case volume do not affect muzzle velocity in a meaningful way for example a using my .284 case with a 183 sierra going from a coal of 3.329 to 3.328, a .001 inch seating depth reduction pushing the bullet further into the case is about a .002 ml of volume reduction of usable case capacity and results in about a .007% increase in peak pressure using 53.8 grains of rl 23 (w/ trued burn rate).
On paper the $5 sensor looks like it is precise enough but my observation so far haven't verified it yet due to my poor choice of material in constructing the pressure vessel. If you're interested in giving it a go the parts list is as follows which is about 40 bucks worth of stuff. Also if anyone has a better sensor suggestion I would be interested.
Arduino mega (or your favorite arduino style)
Bme280
3ml syringe
LCD shield or display of your choice
Some 8mm tubing and fittings I recommend hard plastic tubing or a vessel that will resist expansion or collapse under pressure or in a slight vacuum if you're increasing the volume of the vessel.
Links for weather stations build guides with sketches to run the sensor on the arduino.
https://learn.adafruit.com/adafruit...sure-temperature-sensor-breakout/arduino-test
I guess I should update this thread with my results. The device I built actually worked, but the volume difference on Lapua cases was very small and barely detectable out of the background noise. The biggest problem was the number of variables that would make the device not read tightly enough to be usable. I had to fight with it a lot to get repeatable readings. The main issues were sealing the neck (I used a light grease, but it would leak again within 5 readings or so, and getting differing amounts of grease inside the mouth meant changing the volume), sealing the base around the primer hole (O-ring), getting consistent triggering and throw on the plunger that pulled vacuum into the case and maintaining constant temperature on the device and the cases. Touching the tubing for more than a second caused an immediate change in reading that was larger than any case volume difference because the slightest temperature change would affect it.
I did not pursue getting anyone else to try using it because it was so difficult to get it to be stable enough to do ten cases in a row. When everything was working right, it did indeed give repeatable readings when checking the same case three or four times in a row. Then checking the next case two or three times and getting the same reading would tell me if the second case volume differed from the first one. They would, but not by much. If any of the above factors went wrong I would lose repeatability on the case being tested at the time. Then I would have to re-calibrate and start all over. It was way too time consuming and frustrating. User satisfaction would have been near zero.
I did not pursue getting anyone else to try using it because it was so difficult to get it to be stable enough to do ten cases in a row. When everything was working right, it did indeed give repeatable readings when checking the same case three or four times in a row. Then checking the next case two or three times and getting the same reading would tell me if the second case volume differed from the first one. They would, but not by much. If any of the above factors went wrong I would lose repeatability on the case being tested at the time. Then I would have to re-calibrate and start all over. It was way too time consuming and frustrating. User satisfaction would have been near zero.
Brians356
Silver $$ Contributor
Here's a thought experiment: Ever make a flute out of a pop bottle? You purse lips and blow across the mouth of the bottle at such an angle to create a musical tone. To raise the pitch frequency, add liquid (reduce air volume). A fired case makes an excellent whistle employed the same way, at a much higher frequency. If you take a mixture of 308 Win and 30-06 cases, and whistle them with your eyes closed, you can easily sort the cases by sound alone. But that's a relatively simple task ...
It would be possible to make a fixture which directs a stream of air across case mouths, and measures/compares the tone frequencies produced. However, the cases would need to be precisely trimmed to the same lengths, and the case mouths chamfered/deburred and smoothed identically - not easy to control well enough for our need. Also the air stream is somewhat chaotic. Consider that a flutist controls the pitch by constantly and subtly varying the shape and angle of the air stream, and velocity of the stream, across the mouthpiece. What our ears identify as the sound of a flute, when analysed with an oscilloscope, is actually quite impure with all kinds of shifting overtones and frequency fluctuations. It's likely impossible to get repeatable, usable results by analyzing the sound of our "case whistles". As I said, a thought experiment, but it exemplifies "thinking outside the box" anyway.
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It would be possible to make a fixture which directs a stream of air across case mouths, and measures/compares the tone frequencies produced. However, the cases would need to be precisely trimmed to the same lengths, and the case mouths chamfered/deburred and smoothed identically - not easy to control well enough for our need. Also the air stream is somewhat chaotic. Consider that a flutist controls the pitch by constantly and subtly varying the shape and angle of the air stream, and velocity of the stream, across the mouthpiece. What our ears identify as the sound of a flute, when analysed with an oscilloscope, is actually quite impure with all kinds of shifting overtones and frequency fluctuations. It's likely impossible to get repeatable, usable results by analyzing the sound of our "case whistles". As I said, a thought experiment, but it exemplifies "thinking outside the box" anyway.
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Trying to seal a case tightly enough to pull a vacuum would be a pain. Instead seal the case as tightly as you can with something that has a gage port and raise the temperature of the case 1 degree C the pressure increase would be minute but measurable. Or just inject 1 cubic mm of gas into a sealed case and see how much it increases. I did some work on industrial refrigeration and vacuum leaks are hard to find/seal. You would need a transducer that has a fine resolution of course
Brians356
Silver $$ Contributor
And said transducer is subject to regular re-certification.
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Re-certification is only necessary if you are trying to get a precise unit of measure. Using it as a comparator does not require an exact measure basepoint. It merely requires an accurate transition from one level to the next.
why? Would you be using it for trade ? My digital scale that I use for powder weighing would need certification if I used it for trade, I don't of course. I was just tossing out a what if.
Personally I figure that the burning powder creates such large volume of gas that a relatively small fraction of a percent of case volume would not amount to a gnats fart in a hurricane as far as pressure and velocity. But for those who do care I was just making a hypothetical suggestion, I figure it would be easier to seal a couple of millibar of pressure than it would a to seal a vacuum. Of course you might run into the same issue that the difference would be so small it would get lost in the noise
The OP is on the right track though, gasses behave in ways that are easily calculated and you will get readings as precise as the instruments measuring are capable of
Getting lost in the noise was one of the issues, but I was able to get out of the noise enough so that it worked if I could have gotten past all of the other issues. I learned from several years in the air conditioning industry that sealing vacuum is much easier than sealing pressure (depending of course, on how the seal joint is made). It is true in the instance of pressure inside a cartridge case. Positive pressure will push any sealing surface AWAY from the case, opening up the seal. Negative pressure (vacuum) pulls the sealing surfaces tighter into the seals.
I tend to agree with you about the proportion of difference it would make against 60,000 PSI of ignition pressure. But then, I think that about neck tension as well, and look at how anal lots of folks are about that.
Brians356
Silver $$ Contributor
I'm well aware of that, and anticipated the comment. But it can also go non-linear, meaning transitions from one level to the next are no longer accurate. I concede it will probably remain "close enough" for the purpose, but also renders questionable the real need for it - for our purposes.
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case capacity difference causes velocity difference which causes virtical spread at 700 yd and beyond. load to .02 gr in same size cases will cause smallest virtical groups. 8 fps E. S. or less is possible. measure fire formed cases only before sizing. short range will not show inprovement.
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