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Digital case volume meter

How much would long distance shooters be willing to pay for an accurate digital case volume meter? No more messing with liquid and the associated clean up. Much, much faster volume sorting of cases. I have the design complete and should have a prototype built and tested by Christmas. I will have to machine the parts on my CNC mill.

Digital tubing micrometers can run into hundreds of dollars. Would $250 be too much for something that has heretofore been non-existent and will do the job accurately, quickly and efficiently?

Ron
 
Would need a clue about if, how, and how well it works before consideration.

Of course. I will need a top 1000 yd competitor to evaluate it after completion. A non-disclosure agreement would be necessary.

I searched online for anything similar and the only thing I could find was an instrument developed by automotive manufacturers to measure cylinder volume. It was hugely expensive, in the tens of thousands of dollars, and very sophisticated (computer controlled). Stay tuned.
 
If it is accurate, repeatable, relatively fast and at a good price point, then I think you would have no marketing problems.
 
I'm guessing it won't be in demand. Once you get a good average, even with the wet, inconvenient method, there's nothing further to do. Load for that weight, and shoot them. I did my best to weigh 56 cases of Lake City and 30 cases of Lapua. I got extreme spread of at most 0.5-0.6 grains of water capacity for both brands, with the bell curve being very weighted toward the center of the range. Then I loaded 9 cases of the ones that were all the same capacity, in the middle of the range; and I loaded 9 cases of ones from the extremes of the range (5 of least and 4 of greatest capacity). That was from the Lake City batch of 56 cases. I shot the same load in all the cases, the same way (after one cold bore shot to start the day, consecutive days, tripod and rear Edgewood bag, one minute between shots, all indoors at the same temperature and 100 yards). One group was 0.706" and the other group was 0.712", and the smaller group (although they are statistically identical) was from the group of cases at the extremes of weight capacity. This is a fairly small sample, but I have not heard of anyone else obtaining contrary results, who has done any similar test to this extent. I am retired, and shoot almost every day, and I'd rather reload than eat. Somebody else do the same test, and see what happens. If the result keeps being the same, I doubt demand will justify your effort. As always, I could be wrong. The reason I only shot 9-shot groups is because I only ended up with 9 cases out of the 56 I weighed that were at the listed extreme. That's how steep the bell curve was. I stopped weighing Lapua cases after 30, because they were indeed slightly closer to the center of the range; i.e., 0.1 gr less at both the top and the bottom weight capacity. And as anyone who has done this knows, the measurement error is significant from this method. Even given those statistical concerns, there's no significant accuracy advantage that I could demonstrate to justify sorting by case capacity.
 
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I'm guessing it won't be in demand. Once you get a good average, even with the wet, inconvenient method, there's nothing further to do. Load for that weight, and shoot them. I did my best to weigh 56 cases of Lake City and 30 cases of Lapua. I got extreme spread of at most 0.5-0.6 grains of water capacity for both brands, with the bell curve being very weighted toward the center of the range. Then I loaded 9 cases of the ones that were all the same capacity, in the middle of the range; and I loaded 9 cases of ones from the extremes of the range (5 of least and 4 of greatest capacity). That was from the Lake City batch of 56 cases. I shot the same load in all the cases, the same way (after one cold bore shot to start the day, consecutive days, tripod and rear Edgewood bag, one minute between shots, all indoors at the same temperature and 100 yards). One group was 0.706" and the other group was 0.712", and the smaller group (although they are statistically identical) was from the group of cases at the extremes of weight capacity. This is a fairly small sample, but I have not heard of anyone else obtaining contrary results, who has done any similar test to this extent. I am retired, and shoot almost every day, and I'd rather reload than eat. Somebody else do the same test, and see what happens. If the result keeps being the same, I doubt demand will justify your effort. As always, I could be wrong. The reason I only shot 9-shot groups is because I only ended up with 9 cases out of the 56 I weighed that were at the listed extreme. That's how steep the bell curve was. I stopped weighing Lapua cases after 30, because they were indeed slightly closer to the center of the range; i.e., 0.1 gr less at both the top and the bottom weight capacity. And as anyone who has done this knows, the measurement error is significant from this method. Even given those statistical concerns, there's no significant accuracy advantage that I could demonstrate to justify sorting by case capacity.

Well, that's the entire question then, isn't it? Just how much does case volume variation affect pressure? I did some quick calculations and discovered that a 6mm bullet moved 5 thou deeper into the case displaces .000232 cubic inches of volume. If you convert your .5 grains of water to volume, it is .001977 cubic inches. So, that is equivalent to moving the bullet 8.5 times 5 thou, or 42.5 thou. If you hold case volume constant and let seating depth vary by 42.5 thou, what effect will that have on accuracy? Would not holding seating depth constant and varying case volume by the same amount (.5 grains of water) have the same effect?

I also did a rough calculation on the volume of 1 thou of carbon lining the inside of a 6BR case (I've seen flakes that thick or thicker come out of ultrasonically cleaned cases). If you round off case volume to a 1/2 inch cylinder 1 inch long and calculate surface area, then figure volume of that area times one thousandth depth of carbon, you get .0019 cubic inches, which is about the same as your .5 grains of water.

It seems to me that it would be a statistically significant volume variation, but I've not tested it personally because I never wanted to mess with weighing water volume from a case. Another question with that method is, how uniform is the wetness left behind in each case when you empty the water for weighing? What I'm working on will be a much more accurate measure of case volume. It seems to me that case volume is the last statistically significant cartridge variable to be brought under precise control. I would not expect to see much group variation at 100 yards, but in 1000 yard competitions it could make considerable difference.
 
If it is reliable I hope you do not do much shooting because you will be building them instead of enjoying the sport, I would have at least 2, in this sport 1 is never enough.
Terry Pohl
 
...I never wanted to mess with weighing water volume from a case. Another question with that method is, how uniform is the wetness left behind in each case when you empty the water for weighing?

Um, usual practice is weigh an empty case then fill with water and weigh again; subtract weight when empty from weight when filled.

Measuring case water capacity’s tedious enough without having to weigh the water taken out of a case, let alone how much of it may be left inside.
 
Sounds like a heck of a good time saver to me.
Volume measuring takes a ton of time, but worth every minute of it.
Let me know when there is a pre order list.
CW
 
At the very least, you will produce an affordable tool that can be widely used study the effects of case volume vs velocity/pressure while using a much more accurate methodology than currently used.

I predict that such a tool will produce a measurable improvement in the science of long range shooting, and thereby increase the success of average shooters like myself. I say go for it!
 
Make a prototype, then repeat my test. No one who has posted has shown or mentioned any on-target information that validates the concept. That doesn't mean you should not do a test. I would not go into production without a prototype and on-target proof of concept. My testing was at 100 yards, since that's the longest indoor range I know of. You will not be able to demonstrate a 1,000 yard improvement due to variations in wind, which is greater than the effect of the variable being tested (case capacity), and that will make testing invalid under those circumstances.
 
In response to the post which calculated the equivalent change in seating depth due to the 0.5 grain difference in case capacity, I will point out that those are apples and oranges. I'm not defending my statement. I'm just clarifying that seating depth effect is not equivalent to case capacity effect. Again, my focus is ultimately on what can be shown on a target. If something can't be demonstrated on a target, then for me, it's not something I am going to pursue.
 
A couple of observations with case volume.

I was working some loads for a .223 AR. All Federal cases, Federal primers, CFE223 powder, and LeHigh 55g bullets. Seated to a COL of 2.260" I used 28.4 grains with an average velocity with 10 shots of 3,045 fps. The exact same round seated at 2.300" (+.040) only averaged 3,014 fps. I had to increase the powder to 28.8 grains to get back to 3,050 fps. The rifle has about .150" jump so the seating distance only really effected the case volume.

Using a .308 and 200.20x Berger bullets in Hornady cases, I had to start over with new cases (other needed to be retired). Starting out with new (another lot) of Hornady brass, the velocity fell way off, from 2,535 to 2,490 average. I had to add 8/10 grain of Varget to get the velocity back to where it was. I measured the cases after firing and the internal volume averaged 7% more in the new cases.
 
If it was accurate I'd buy one. Smaller cases like the 223 can vary .5gr of capacity also which really matters with only 24gr of powder.
 

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