First try @ volume testing

[Topwater]

I tested Norma 6XC brass today. Since this is my first attempt I could use some feedback. This was my process:
trimmed brass
chamfered necks
neck sized
wet tumbled
primed with cleaned & tumbled primers with anvils removed ( I was advised by an engineer to insert
( primers upside down to have a more uniform volume)
weighed each brass
filled with drops of water
weighed brass again
calculated weight of water ( I’ve read that alcohol is a better medium, not sure )

After all the effort, what do I do with the results other than sort the brass?

 

[Coyotefurharvester]

Weigh dry brass, then weigh filled.

 

[Straightshooter1]

I tested Norma 6XC brass today. Since this is my first attempt I could use some feedback. This was my process:
trimmed brass
chamfered necks
neck sized
wet tumbled
primed with cleaned & tumbled primers with anvils removed ( I was advised by an engineer to insert
( primers upside down to have a more uniform volume)
weighed each brass
filled with drops of water
weighed brass again
calculated weight of water ( I’ve read that alcohol is a better medium, not sure )

After all the effort, what do I do with the results other than sort the brass?

Inserting old primers upside down is what I do and works very well. I'll put a case on my electronic scale and zero the scale. I'll then fill the case until the water forms a dome at the mouth and wick that dome with a corner of a piece of paper towel until the water is level with the mouth (making sure it's not concave by shining a little flashlight on it from behind so I get a clear view). Since I zeroed the scale, the scale will show the weight of the water for that case. Then I simply do the whole process over for each case.

Afterwards, if you're using various brands of brass, you can get an idea as to the difference that can help you adjust your load, if need be. Like with Winchester brass with its thinner case walls, the volume will be substantially greater than than many other brands of brass.

 

[RegionRat]

Straight alcohol isn't the same density as water.

We use water to convert weight directly to volume because of the theory that the density of water allows for the weight in grams to convert to the case capacity because water is near 1 g/cm^3. So, for every gram of water you would expect 1 cc of case volume. If you use something with a different density, you would need to multiply that liquid weight by a conversion factor to get case volume.

A few drops of IPA are sometimes diluted into water to adjust the polarity and surface tension of the water since the brass can often have a contaminated neck that affects the ability to release trapped bubbles and get a flat meniscus. A few drops of detergent can also be used if required since it will have a negligible effect on the density. Surface tension can make bubbles hard to release or a meniscus difficult to stay flat and there are differences in clean virgin brass and fired brass based on how those were cleaned.

What to do with those results? That is up to you.

I would suggest you read up on the internal ballistics and the effects of internal case volume on pressure and velocity. To get a negative effect on the vertical performance, the difference in your brass as a independent variable would have to be large enough to shift your group or impact. So your testing would attempt to prove to a statistical significance that the difference in internal case volume affects your spread or POI.

Your shooting an testing has to be on point to detect the difference between fireformed and virgin brass, but is isn't too difficult to show the difference between some brands that have different web thicknesses. If you start to care, then learning how to measure your case volume and keeping track of different brands of brass and such isn't a bad thing to do.

 

[JohnKielly]

Why test volume of unfired brass that hasn't been formed to your chamber? Who knows if it will be valid after firing.

 

[RegionRat]

Why test volume of unfired brass that hasn't been formed to your chamber? Who knows if it will be valid after firing.

When in the rat race and trying to keep up with the demands of life, it isn't rare to have to load virgin brass cause you don't have fireformed at hand.

There is also some insight in knowing the difference due to fireforming. When that difference gets too large, I am on guard for sizing problems.

 

[piie]

Unless you're planning on using the volume readings in something like quickload, the density of the fluid you use does not matter - you are doing a comparison for sorting and grouping purposes. Adding IPA or just a bit of dishwashing soap will help you to get a perfectly flat meniscus to make it easier to measure a consistent "full" value.

If you want an accurate volume reading for quickload, it's arguably also not that critical ( just don't use cement ) since there will be variances between your cases and you will end up using an average weight for your quickload input. But you could just weigh a known volume of the additive liquid (or google it), and then do some basic calculations on what your scale readings translate to water volume wize. Of course, all of this is moot if you don't have a scale that can measure the mole on a tick's ass, or a pipette/burette/measuring flask that can give you accurate volume readings of your mixture - but I'm fairly sure (again, as long as you choose not to use cement or essence of depleted uranium) that the water volume values you get will be "good enough" even for use in quickload.

And yes, I would also re-do whatever volume measurements I did on virgin brass after they are fully fireformed, just because my spidey senses will always tell me there should be a difference now... and my other senses would tell me that after going through all that trouble, not annealing after each firing would just be cause for all of the above to be a waste of time.

 

[Topwater]

This experiment was done on Norma brass that had been fired four times in the same chamber. I annealed it prior to trimming. I did not add a drop of detergent to the water. Thanks for suggesting this. Another thing I will try is the backlighting trick to more easily see the “meniscus”.
From all I have learned, the question still remains……….do I now just sort the brass into like volume capacities? This appears to be the end goal of all this. If that is the case, how close to exactly the same should I sort this brass? Is one grain close enough? My most discriminating scale will only weigh to 0.02 grains, not grams. My main goal is to eliminate all the variables possible to aid in 1000 yd. benchrest competition. Thanks again for all the input.

 

[piie]

This experiment was done on Norma brass that had been fired four times in the same chamber. I annealed it prior to trimming. I did not add a drop of detergent to the water. Thanks for suggesting this. Another thing I will try is the backlighting trick to more easily see the “meniscus”.
From all I have learned, the question still remains……….do I now just sort the brass into like volume capacities? This appears to be the end goal of all this. If that is the case, how close to exactly the same should I sort this brass? Is one grain close enough? My most discriminating scale will only weigh to 0.02 grains, not grams. My main goal is to eliminate all the variables possible to aid in 1000 yd. benchrest competition. Thanks again for all the input.

Yes, the idea is that cases with the same case volume will produce better consistency ito velocity when loaded exactly the same in all other aspects. That, and the fact that you should have a good value to enter into QL if you choose to use it.

How to match/divide the cases based on the volume measurements will probably be determined by what you observe ito spread when measuring and how many cases you have - AND - how much of a difference you think it would have if you choose to group by 0.1 gn instead of 0.5 gn for example. This should be easy to test though by loading a few batches and shooting them to see if it makes any difference on target or ito ES/SD.

It is however probably good to just ask around, or have a look at what guys like Erik Cortina or F-Class John does (to anem afew) - I doubt (from recalling) that they bother with sorting brass by either weight or volume anymore. I've certainly stopped since standardizing on good brass like Lapua - I literally don't do anything to my brass anymore - just fireform - but the "good guys" go an shoot competition with virgin lapua brass - so that should really tell you the whole story right there...

 

[mikecr]

After all the effort, what do I do with the results other than sort the brass?

What you've done to this point is meaningless.
Fire form your brass several times and take valid measurements.
Then, consider culling offenders.

 

[gme]

I tried that once, then fired groups with cases that were carefully loaded using brass from the center of the bell curve and brass mixed from each end of the bell curve

 

[timeout]

What you've done to this point is meaningless.
Fire form your brass several times and take valid measurements.
Then, consider culling offenders.

Look at post #8. He says that he has fired it 4 times.

 

[358WCF]

I read on the internet (so it might be true) that for truer water weight that tap water should sit for 12 hours or more to allow the little bubbles to work their way out of it. Never bothered to check the accuracy of that statement, but there it is.

 

[SSL]

I read on the internet (so it might be true) that for truer water weight that tap water should sit for 12 hours or more to allow the little bubbles to work their way out of it. Never bothered to check the accuracy of that statement, but there it is.

Probably true if you are looking for the absolute weight of water itself, but in weighing for case volume any liquid will work as long as it is the same type liquid for each case.

 

[RegionRat]

@Topwater since you put this into the context of 1000 yard benchrest....

Some folks will shoot no turn, others turn, both can win... same goes for things like weighing primers or sorting case volume...

You will just have to fireform your cases several cycles to settle their growth and then establish the statistics for your batch. Then as Gary Eliseo suggested, form a group with the middle, and compare it to the extreme of the tails. Or, if you have enough that you can make two different strings from the two tail extremes, you can test to see if that disturbs your performance.

If your rig and your process can be improved by the sorting, then nobody will talk you out of it. On the other hand, if your brass is so good that even the max and min volume doesn't disturb the performance, well why would you?

Many decades ago, the quality of the brass we used for accuracy work necessitated it be made from batches that would easily ruin your performance if you didn't prep and cull them. But, these days, there are many folks who just weigh their cases to eliminate defects cause the batch is held so tight that screening for internal volume isn't getting them better groups. I have had batches of Lapua in the range from 223 to 6 BR where the ES in grains for the whole batch was 3 grains. Since I shoot sling, but test from the bench, I can say I split that batch into two halves and sleep well in terms of the difference that could make at 600 to 1000.

You will have to test for yourself based on the brass you can get.

 

[mikecr]

Ultimately it's not about volume itself.
With same volume -at same thickness -at same alloy & hardness, the cases should make up chamber clearances on firing with the same energy.
That's what you want.
The bigger the clearances, the bigger the affect of this variance.

You could pick an arbitrary bell curve percentage(something reasonable), or see if you can shoot the differences in full span, and go from there.

 

[Ned Ludd]

I generally weigh the fully-prepped but empty cases prior to loading, then determine water volume after firing. Determining water volume after case prep, but prior to firing will only give the water volume of a re-sized case. What you're after is to determine the water volume of a fired case, meaning a case that has fully expanded to fit the chamber, which can also referred to as the pressure cell volume because it is the the effective volume in which the powder combustion takes place.

In order to determine water volume, it is unnecessary to use additives such as alcohol or detergent. In fact, such additives increase the likelihood of forming bubbles inside the case that will increase variance within the measurements. I deprime the cases first, then re-insert the primer backwards to minimize any getting water into any additional space past the flash hole, which can introduce additional weight/volume variance. Tare the balance to the empty case. Fill the case almost to the top of the neck with an eyedropper, or simply by dunking the case in a bowl of tap water and drying off the outside carefully with a paper towel. Place a fingertip over the case mouth and shake it downward several times to move any bubbles inside to the top. Using the eyedropper or a drop of water on the fingertip, fill the case to the top using a lamp of some sort to backlight the meniscus. The back lighting makes it very easy to visually determine when the case is full with the meniscus completely flat. Re-weigh the case to determine the water weight. Use a value for the density of water of 1.000 g per cubic centimeter/milliliter, or 15.4324 gr per cubic centimeter/milliliter. Frankly, the units don't really matter. You can find whatever conversion factor you need online, so whatever units your balance is set to will work just fine. I posted a more detailed version of the method I use here at A.S. some time a ago:

Case Volume Determination (pic heavy)

Readers here will see many, many posts regarding determination of case volume. There seem to be about as many different methods as there are posts on the topic, such as using detergent or alcohol mixed with the water, how the primer pockets are sealed, how "full" the case should be filled...

forum.accurateshooter.com

Once you have determined the water volume of some cases, you can then investigate several interesting questions. For example, does the internal volume you measured correlate with velocity? In other words, as case weight increases, does velocity also increase for a given charge weight? It should. However, sources of limiting error become critical in such analyses. If you plot case weight versus case volume, you should observe a very nice linear correlation. I do this regularly with all my brass preps and routinely observe this to be true. Case weight of fired cases does have a strong linear relationship to case volume. Nonetheless, various sources of error in case volume determination and volume of the extractor grooves/primer pockets means that not all of the data points within your case weight versus case volume scatter plots will fall directly on the best fit curve of the data. There will always be some outliers. In general, the better your technique in determining water volume, the more closely the data points will be to the linear curve fit. But it is important to re-iterate that there will always be some outliers. Below is a graph for 10 cases I did just a few days ago. You can see from the "R" value (0.99) of the linear curve that the data show a strong linear correlation between case weight and case volume. But there are clearly some outliers that do not fall directly on the best fit linear curve. Those anomalies need to be taken into account when using such data to interpret real-world results, such as velocity. It is always interesting to try to determine whether outliers from the mean velocity might be caused by case volume variance. For example, might that one velocity reading that was noticeably higher than the others in the string happen because of a case that had markedly lower volume (higher weight) than the others? It is certainly worth the attempt to establish such correlations, but just be aware because of the outliers that it may not always be possible to make such conclusions in every instance due to the outliers/sources of error. However, it is still a good learning experience, IMO.

Because of the limitations (sources of error) inherent in determination of case water volume, I generally do not try to squeeze too much out of the resulting data. Picking it over with a fine tooth comb may not be the best investment of your time. Because I am 100% convinced in the general correlation of case weight to case volume, I will typically sort a Lot# (batch) of cases into three or four distinct weight groups. Even with the presence of a few outliers, there is a very high likelihood that the case volume variance among the individual weight sort groups will be smaller than the case volume variance of unsorted brass. In other words, the case volume variance of weight-sorted cases is almost always tighter than if I do nothing at all. That is really all I am interested in accomplishing...just tightening up case volume a bit within the sorted brass weight groups. I do not claim there can't still be a few outliers, or that all of the sorted cases will somehow exhibit perfect weight to volume correlation. That isn't so. But they will usually be better than if I did nothing. That is what I really mean by not trying to interpret the case volume/weight data to too fine a level. All you're really trying to do is improve the consistency of case volume within the sorted groups, not to make it perfect, or make conclusions about individual cases that may or may not be true depending on how close to the best straight line curve fit they fall. For such an exercise, weighing cases is a good way to go. It is fast and very simple to do, and the sorted case volumes will jot only never be worse than the unsorted batch of brass as a whole, they will usually be more consistent. So you get a small but measurable benefit for relatively little work.

 

[Topwater]

I sorted fifty brass by weight of water volume. It was tedious to say the least. There will have to be a marked improvement in groups on paper for me to sort any large amount of brass. I plan on comparing group sizes between the central bunch and those on the low and high ends. This may or may not convince me that the effort is indeed worth it. Thanks to all who have shared constructive thoughts on the process. The folks on this site have always been most gracious in helping me in these learning processes.

 

[Ned Ludd]

When you load those sorted cases up, I'd suggest starting with comparing velocities for a few cases from the very largest and smallest volumes within the total range. That will give you the best chance of detecting a difference in velocity caused by case volume variance, if there is going to be one. Just a few days ago, I fired a charge weight test using the same .223 Rem brass prep I used to illustrate the linear relationship between case weight and case volume in Post #17 above. I typically do not sort cases by weight during load development, only for matches after a final load has been obtained. I figure the variance during testing is acceptable. if I can get the velocity and precision working acceptably without sorting them, those parameters will only improve when I sort the brass for a match, or at worst, stay the same. For that reason, the cases used in this charge weight test were not weight-sorted, although I did determine the weight of each de-primed case afterward.

In any event, what I again observed from this charge weight testing experiment is that at any given charge weight, velocity outliers (high/low) were typically associated with the very heaviest or very lightest cases. Variance in velocity was harder to clearly associate with cases having weights somewhere closer to the middle of the overall weight range. This is more anecdotal information supporting my belief that extreme variance in case weight/volume can readily be detected in terms of the magnitude in its effect on velocity. The effect of minor case weight/volume variance on velocity become "lost in the noise", so to speak. In other words, minor case weight/volume variance is not the limiting (largest) source of error in velocity and can be masked by the other factor(s) that are limiting sources of error. Here is a small example from a single charge weight of that testing to illustrate the point:

Case weight (g) Velocity (fps)
6.1691 2704
6.3409 2724
6.3150 2738
6.1993 2716
6.1315 2698

Note that the two cases in the 6.3+g range yielded the highest velocities, whereas the lightest case (6.1315 g) yielded the lowest velocity. In contrast, the velocity of the 6.3150 g case was slightly higher than the 6.3409 g case. The caveat to these types of exercises is obviously the very small sample number. Nonetheless, I have previously determined velocity using slightly larger numbers (10 each) of cases from the heaviest (>6.3 g) and lightest (<6.15g) cases within the Lot#, and the velocity variance trend was always the same. On average, the heaviest cases gave velocities that were ~25-35 fps faster than the lightest cases. I have also observed this trend often enough with smaller sample groups that I believe it to be a relatively safe assumption. Obviously, the relative volume of the cartridge used will be a factor. It is not too difficult to see the effect of case volume variance with the relatively small .223 Rem cartridge. In my hands, as the cartridge capacity increases, the effects seem to become less obvious.

With this particular .223 Rem load, I can usually obtain ES values (5-shot groups) of around 15-20 fps. What I believe this indicates is that the case weight/volume variance has to be large enough to cause readily detectable and statistically significant velocity changes over other inherent factor(s) that also generate velocity variance such as primers, charge weight variance, neck tension, bullet weight, etc. In other words, starting with the most extreme variance in case weight/volume (i.e. the smallest and largest volume cases within the sort) will give you the best chance of detecting an effect on velocity, if it actually can be detected. If you do such a test and obtain a statistically significant difference, that also implies that sorting cases by weight or volume might be beneficial even within a narrower case weight/volume range where it is much more difficult to detect above the background noise (i.e. other factors that cause velocity variance). In such a case, it can be argued that if the velocity variance due to case volume variance is small enough to be masked by other factors also causing velocity variance, it can be ignored. However, sources of error are often additive. So it can also be argued that sorting cases by a weight/volume increment that is small enough it is difficult to detect is effectively the same as removing that source of error. I favor the second interpretation. Removing a slightly smaller source of velocity error when other larger sources of error are also present is unlikely to provide instant gratification or readily observable differences in terms of velocity ES/SD values, but it will never make your results worse.

This is exactly what I was trying to point out in my earlier post. Sorting cases by weight/volume into three or four distinct sort groups can really do two things for you. The first and foremost is to remove the extreme velocity outliers caused by case weight/volume variance. The second and less obvious or noticeable result is to minimize a smaller source of error that, even if hard to detect over other sources of error, is nonetheless present. The first of these benefits is usually easy to detect, the second requires a little faith. As you noted in your post above, determining case water volume in a precise and accurate manner can be extremely labor-intensive and tedious if you are working with large numbers of cases. In contrast, weighing cases as a surrogate for volume determination is relatively simple and does not require huge amounts of time. Thus the practical benefit of one approach over the other can often be weighed in terms of the intended use. Does your shooting typically require large numbers of cases? Or can you get by with a much smaller total number cases? In the first example, sorting cases by weight is probably the better approach. This is what I do for F-Class matches, and I don't concern myself with keeping the weight-sorted cases separate after firing them. This makes brass prep easier as I do it in large batches. However, it also means I have to weight sort the cases after each prep. I don't find that to be too much trouble. In the second example, it shouldn't be too painful to sort a few cases by volume, which is the more accurate/precise method, and then keep the weight groups separate during subsequent brass preps so you don't have to go through the volume sorting process more than once.

 

[mikecr]

If you FL size much all this will change (weight and vol, from hardening & trimmed away).