Determining Case Volume with Water

[MVW]

In reading a number of reloading forums, I have seen frequent mention to measuring the volume of brass by weighing it full of water. However, I have not seen a description of how to actually do it. As a practical matter, does anyone know how you perform this task? I assume one does it after the first firing while a spent primer is still in place - perhaps not...

Mike

 

[Dans40X]

Internal case volume-
Compile all the data that you can by weighing primers,primer cups,fired,unfired & sized cases,then repeat w/ internal volume test.
Unfired Primers weigh approximately 1/2grain.
Unfired 50BMG primers weigh approximately 19.5grains.

I seat unfired primer cups w/ compound/anvil removed upside down in pockets.

 

[johned]

Why not use your tare weight function to null out the weight of each brass with a fired primer installed or tape over the bottom?

If you use a crono and can get the velocity to a consistent ES SD that is all that is needed. Always gonna be some variation from shot to shot so multiple crono readings on the same piece of brass is needed to find the average. Assuming you crone you shots anyway.

 

[Steve Blair]

Take ten fired cases and weigh each one without water. Record the weights. Fill each case with distilled water so that the meniscus is flat across the mouth. Weigh each again, subtract the case weight and average the water weight of the ten. Record that number and use it in software like QuickLOAD to obtain more accurate predictions. If you are not using software the allows entering the case volume, there is little point in the procedure.

 

[tripcrow]

Here’s what I do:
Fire cases once or twice in chamber they’ll be used.
Deprime prepped cases.
Place cases in a marked loading block.
Weigh each case and record on a large sheet of paper.
Prime cases and record weight again.
Fill and empty each case to get inside carbon uniformly wet.
Fill each case from a slightly warm very slow flowing tap. Cold water will cause condensation to form on the outside of case.
Level off top off case uniformly with the back edge of a knife.
Use paper towel to wipe off any outside water.
Weigh filled case and record.
Empty case and weigh again.
If weights are close record average. If not weigh again till you’re sure you have the correct filled weight. It is easy to be off by .2g if you get an inside bubble.
Subtract difference between filled and empty case.
Sort out &/or separate to your satisfaction.
Deprime and dry cases.
Approximately 4 hours for 2 people to do 100 rounds.


Here’s what I found out:
Now depending on how critical your requirements, my experience has been a good couple of properly weight sorted boxes of Lapua 6BR brass, even wildcats made from it, gain little from H2O sorting. If you sort out the odd light and heavy 10%-20% of the cases and leave the middle 80% or so that weigh within +/-.5g of each other, you should be under +/- .1g water volume. While the mid-weight cases will not show a consistent weight/ volume correlation it is rare that any of those middle weight Lapua cases will be way out of norm in their case volume. But understand that by weight sorting out the light and heavy cases you’ll be losing some good average volume cases. On the other hand those 10%-20% light and heavy cases make up most all the cases that’ll have radically different volumes. So don’t expect too go out and buy and sort 500 cases and have the lightest +/or heaviest 50 or so that have a weight difference of only .5g to be close in volume. It doesn’t work like that. You’re after the mid-weight cases if you’re going to be lazy, take a chance, and not volume check them.

With other makes, or maybe even calibers, of brass the case weight to case capacity correlation is far less and it’ll be much more likely to have a mid-weight case that’ll be way off from having an acceptable volume.

 

[Steve Blair]

Bill, [br]
I assume that you must be a benchrest shooter. The thought of measuring case volume on 500-1000 cases for High Power or F-Class is unappealing. I weight sort for the same reason you do, to push the average more toward the mean. With as many cases as I load, 100% case volume measurement is a bridge too far. Even so, by weight and case wall sorting and all other usual prep, I can sometimes hold 1/2 X-ring vertical through a 20 shot string at 1000. [br]
Just curious: Are you also sorting by case wall thickness?

 

[jlow]

One of the problems with this method is that “regular” water has significant surface tension. What this means is if you fill a case and look at the opening of the neck, you will see that the surface of the water is not flat no matter what you do but convex or concave in nature. It’s the reason why a drop of water on say a glass surface does not coat it with a thin film but bubbles up like a jelly bean. You cannot trim this off with a knife as this will drop the water level below the neck level.

One method I heard about but have not tried is to add some ethanol to the water. Ethanol drops the surface tension of water and allows you to fill the case so that the surface of the water at the neck has a relatively flat surface. Not sure about the exact percentage but I am sure someone can tell us of their experience.

 

[Nomad47]

QuickLoad says to use FIRED cases and leave the spent primer in.

 

[Steve Blair]

One of the problems with this method is that “regular” water has significant surface tension. What this means is if you fill a case and look at the opening of the neck, you will see that the surface of the water is not flat no matter what you do but convex or concave in nature. It’s the reason why a drop of water on say a glass surface does not coat it with a thin film but bubbles up like a jelly bean. You cannot trim this off with a knife as this will drop the water level below the neck level.

One method I heard about but have not tried is to add some ethanol to the water. Ethanol drops the surface tension of water and allows you to fill the case so that the surface of the water at the neck has a relatively flat surface. Not sure about the exact percentage but I am sure someone can tell us of their experience.

It is actually pretty easy to obtain a flat meniscus that can be verified optically by sighting across the surface at a shallow angle. Use a paper towel at the case mouth edge and wick small amounts until the surface is flat. [br]
Ethanol has less than 80% the specific gravity of water and corrupts the data obtained.

 

[Erik Cortina]

I put a drop of dish soap in the water to break the tension in the water. Then I use a cyringe with a needle to fill cases. I get pretty consistent results that way.
And yes, a flat meniscus is obtainable. And no, I do not do all the brass that I use for F-Class. I only do it to obtain case capacity to use with QL.

 

[Cigarcop]

I put a drop of dish soap in the water to break the tension in the water. Then I use a cyringe with a needle to fill cases. I get pretty consistent results that way.
And yes, a flat meniscus is obtainable. And no, I do not do all the brass that I use for F-Class. I only do it to obtain case capacity to use with QL.

Thats exactly what I do, the syringe works great, just go nice and slow and no bubbles will be present and the top will be nice and flat.

 

[jlow]

Yes, I know the specific gravity of ethanol is not the same as water and so it will distort the values a litte but of course if you know the % of ethanol you put in, you can easily adjust for it.

In the end, you are not going to get super accurate numbers for this type of measurement since the case mouth is pretty wide (the narrower the better for accurate volumes measurement i.e. like a volumetric flask for those who knows of these) and it will be difficult to get a consistent meniscus since the case is not transparent. But the fact is it will probably get you the value you need to compare to the much more accurate weight value in terms of trends.

 

[kelbro]

You don't even need to know the percentage of ethanol (I use a little rubbing alcohol in my distilled water). The weight you observe is just a relative number. If case B holds 85gr of your blend and case A holds 85gr...

 

[Nomad47]

It matters when you use QuickLoad. Granted we're likely splitting hairs here.

 

[kelbro]

QuickLoad, while a great tool, is not a measurement tool and its approximations have some fudge factor averaged in.

 

[spclark]

All I can add to this discussion is to tap cases gently on a hard surface once you've filled them up to the shoulder/neck point. This helps knock loose any bubbles that might otherwise distort your numbers. Then fill to neck rim & use a knife edge to level excess.

Ethanol (denatured alcohol or vodka, though I have other uses for the latter) will work in low concentrations. I use dishwashing liquid - just a drop in 8 oz. - and a syringe as described. Typically I measure fired cases with the primers still in but if I'm really looking for critical numbers I'll decap, use the wet SS media method for case cleaning, then stick a fired primer into the pocket backwards (easy enough if you're patient) then weigh the case empty, again when filled then do the math.

Good enough for my need to compare case volumes, not yet a QL user though I'm tempted....

 

[Steve Blair]

QuickLoad, while a great tool, is not a measurement tool and its approximations have some fudge factor averaged in.

Yes, it is a predictive tool and that's why it is important to use accurate, empirically derived data for key parameters like case volume, powder burning rate, bore dimensions and seating depth. When used properly, QuickLOAD can save a lot of money developing loads, choosing components and making design decisions.

 

[RJinTexas]

When I called Quick Load for advise I was instructed that I needed to measuring cases with the water level both convexed and concaved to get the average volume.

RJ

 

[Nomad47]

When I called Quick Load for advise I was instructed that I needed to measuring cases with the water level both convexed and concaved to get the average volume.

RJ

I'm curious. Is the difference significant?

 

[kelbro]

QuickLoad, while a great tool, is not a measurement tool and its approximations have some fudge factor averaged in.

Yes, it is a predictive tool and that's why it is important to use accurate, empirically derived data for key parameters like case volume, powder burning rate, bore dimensions and seating depth. When used properly, QuickLOAD can save a lot of money developing loads, choosing components and making design decisions.

How do you measure powder burning rate??

I agree that it's a good tool and saves both time and components.

Where I disagree is that the factors are precise enough to worry about the meniscus on a case volume measurement when lot to lot variation of powder is estimated (Hartmut's own disclaimer). The program requires you to tweak parameters like burn rate and friction-proofing coefficients to match your measured velocity. The dox even recommend changing case volumes.

Great program but don't get too caught up in it. It's a modeling program.