measuring water capacity- care to share your tricks?

[wolfman]

On the surface of it, checking water capacity doesn't seem too complicated, but as I get thinking about it, I'm curious about how folks actually go about it. I'm guessing fill with a syringe, and place carefully on a scale, but how hard is it to fill to the same level? Is surface tension bulge an issue?

 

[Lapua40X]

The "bulge" of surface tension does influence the mass but it should be essentially uniform over all of the cases tested so the variable remains constant.
There are two methods for calculating the differences in capacity that I'm aware of.
1. Fill the case, tare a container on the scale and pour the water into it to determine its weight.
Then empty the container, dry it, obtain another tare and repeat.
2. Obtain the tare weight of the case, remove it from the scale and fill it, then put it back on the scale and do the math.
Frankly, I prefer the first method ....................

 

[CatShooter]

On the surface of it, checking water capacity doesn't seem too complicated, but as I get thinking about it, I'm curious about how folks actually go about it. I'm guessing fill with a syringe, and place carefully on a scale, but how hard is it to fill to the same level? Is surface tension bulge an issue?

I use a case that has been fired 3 or more times, and only neck sized. Then I fill it with water and remove the curved bulge with a piece of tissue paper.

That way, you get the case volume as applies to your gun - if you have a very tight chamber the functioning volume will be less than a gun with a bigassed sloppy chamber.

<edit>

If you fill the case with water, and then dump the water on a scale, you will not get repetitive measurements, because some of the water will stay in the case as drops or surface wetness. Weight the case first (or tare the case first), fill it with water, and then weight them both again. That way, you will get the weight of ALL the water, and nothing else or no water missing.

 

[stool]

1 cc = 1 gr at 77f/25c if my memory serves me correctly, so warm water.
case as ready for reloading( however you do it, neck sized, fl or whatever)
seat a fired primer upside down to seal the base of the case.
tare on your electronic scale or write down the weight.
slow fill with warm water. tap the case to release any air bubbles, tissue or q tip to reduce the meniscus to as flat as possible.
weigh....electronic scale will give a direct readout, else do the math from empty weight.

log the data.

 

[jlow]

Water actually is not the best liquid for this application since it has high surface tension and so you will get that meniscus (what the others are calling curve bulge).

The best liquid is actually rubbing alcohol since it has much lower surface tension. Use fired brass with primer, put on balance to get weight, tar the balance so that it reads zero. Fill case with rubbing alcohol with 1 mL open syringe (no needle) until it is almost full. Add rubbing alcohol with syringe with 28 gauge needle attached with tip submerged under the surface and look at the top of the case at an angle with head mounted magnifier (like a Donegan DA-7 OptiVisor) with a light in the background. When the case is not full or over filled, you will see a reflection of the light on the surface of the meniscus. When it is full and flat, the light reflection will go away. Note weight on scale, that is the weight of rubbing alcohol in case. If you want actual volume, you can do the conversion using density of Isopropyl alcohol of 0.786 grams/cc and water 1gram/cc keeping in mind that rubbing alcohol is 70% Isopropyl alcohol and 30% water.

Keep in mind that this method is only as good as your technique. As a rule, always measure 3x the same case. You do this by sucking out a little of the rubbing alcohol after one measurement and then add rubbing alcohol again to the same case and see what weight you get when you think the surface is flat. With LC09 223 cases, average volume fill weight is around 27 grains, you should be able to get between 0.02 to 0.1 grain variance between the three readings with this technique. Average the three values to get a more accurate estimate. When I did it, 20 cases had a variance of 0.24 grain in terms of volume so you can see if you don’t measure three times and accurately, your numbers may not mean much i.e. the noise of the measurements may be larger than the volume difference.

 

[Jeremy(WI)]

1 cc = 1 gr at 77f/25c if my memory serves me correctly, so warm water.
case as ready for reloading( however you do it, neck sized, fl or whatever)
seat a fired primer upside down to seal the base of the case.
tare on your electronic scale or write down the weight.
slow fill with warm water. tap the case to release any air bubbles, tissue or q tip to reduce the meniscus to as flat as possible.
weigh....electronic scale will give a direct readout, else do the math from empty weight.

log the data.

1cc of water = 1 gram

I had to look it up

 

[Lapua40X]

... I fill it with water and remove the curved bulge with a piece of tissue paper.

The reason I don't use that method is because the capillary action of the tissue paper is difficult to control and it can pull more from the case than just the convex meniscus liquid, making it difficult to detect the level of the liquid once the convex meniscus has been eliminated.
While I do not believe that the liquid capacity method has any real value for determining case capacity for the purpose of learning which cases in a given sample I can load up with more powder, I do find it useful for sorting cases when the objective is consistency in seeking the most accurate loads.

 

[stool]

with the warm water and a tissue edge or q tip..i have no issues getting a flat meniscus......
have i ever had to do it over , yes, is it time consuming, no.
cheaper and quicker than alcohol......

each to their own

 

[21shooter]

Hi, A small video , NO MESS Easy http://youtu.be/kR69vKiYX1E
Thanks, John
http://www.21stcenturyshooting.com/Primer_Pocket_Plugs.php

 

[Mega]

Try adding a drop or two of detergent to the water you use to modify the surface tension of the water.

 

[stool]

he did not tap the case to ensure no air trapped, he never even look at or mentioned meniscus....
not my accuracy..

Hi, A small video , NO MESS Easy http://youtu.be/kR69vKiYX1E
Thanks, John
http://www.21stcenturyshooting.com/Primer_Pocket_Plugs.php

 

[Jeremy(WI)]

Try adding a drop or two of detergent to the water you use to modify the surface tension of the water.

It shouldn't take much detergent at all but how much does it affect the weight. I might try a few things as I use a ultrasonic to clean my brass, there might be enough detergent remaining inside to reduce the surface tension of water to get reliable readings on the scale

 

[Clod-NC]

Hi gentlemen

Very interesting thread indeed,I sure don't want to disturb,but then,please, tell me what you do with the irrelevant part of the case constituded by the entire neck portion of it,do you subtract it,and if so, how do you measure it?My remarks non withstanding,I did this at a certain time of my approach of the whole process, I believe the easiest way would be the detergent method(2 or 3 drops in a syringe will do,just like when I used to process black/white photo films in my youth,to avoid the drying water leaving white streaks on the acethate support).Have a lot of fun with it gentlemen,and stay safe and cool.

 

[Webster]

Why is there a need to measure water capacity? I usually see it used to compare similar cartridges like, 6BR, 6 Dasher & 6BRX. If you had a pile of 6BR cases the same brand wouldn't they all have the same water capacity? If they are the same what can you do with the capacity number? If all the cases are made to the SAAMI external dimension they can only vary by brass thickness at various locations. SAAMI only gives case external dimensions not internal. What I am getting at is why not simply weigh the cases instead of determining internal volume. If the cases have a standard external dimension there should be a direct relationship of weight to internal volume. You can weigh cases more accurately than determining water volume and it's quicker.

 

[Raythemanroe]

Why is there a need to measure water capacity? I usually see it used to compare similar cartridges like, 6BR, 6 Dasher & 6BRX. If you had a pile of 6BR cases the same brand wouldn't they all have the same water capacity? If they are the same what can you do with the capacity number? If all the cases are made to the SAAMI external dimension they can only vary by brass thickness at various locations. SAAMI only gives case external dimensions not internal. What I am getting at is why not simply weigh the cases instead of determining internal volume. If the cases have a standard external dimension there should be a direct relationship of weight to internal volume. You can weigh cases more accurately than determining water volume and it's quicker.

I think it is because some people believe the internal volume may have an effect on pressure and that sorting this way will help with velocity spreads therefore leading to better accuracy. I like this idea better then just sorting by weight, because I don't know where the weight was lost or gained and if it will have any ill effect on accuracy or not.

 

[Webster]

I think a lot of cases vary in thickness between brands in the case head area. Weighing in this case wouldn't be related to volume. Different % of zinc (brown box vs blue box and different brands). I don't shoot competition so I am not to fussy. My 6BR shoots .25 to .35 groups which is better than needed for GH. Do you find volume differences among cases from the same box of 100 cases?

 

[stool]

first saami is a spec with a tolerance...THAT MEANS THEY MAY NOT ALL BE THE SAME and still be in spec.
manufacturing tolerances add up and be for you know it.....no they are not all the same.
my most current batch of new winchester 223 brass varied from 91 gr to over 95 grains....they aint all the same.
in a quest for accuracy, consistancy is a big factor down range, the further the range the more consistant you need to be.
out of a prior lot of 500 pcs of winchester brass, i found 30 that had the same internal volume after fire forming.

it all depends on your desires and personal definition of "accuracy".

Why is there a need to measure water capacity? I usually see it used to compare similar cartridges like, 6BR, 6 Dasher & 6BRX. If you had a pile of 6BR cases the same brand wouldn't they all have the same water capacity? If they are the same what can you do with the capacity number? If all the cases are made to the SAAMI external dimension they can only vary by brass thickness at various locations. SAAMI only gives case external dimensions not internal. What I am getting at is why not simply weigh the cases instead of determining internal volume. If the cases have a standard external dimension there should be a direct relationship of weight to internal volume. You can weigh cases more accurately than determining water volume and it's quicker.

 

[jlow]

Regardless of which process you use, remember that the most important thing about doing this is not how easy it is but accuracy/precision because unless your technique and data is good, it’s just a useless exercise.

Most people look at my technique description and their eyes just glaze over, I understand this since they don’t do precision measuring for a living and don’t understand why it is important. However, this may be one reason why most people who do the volume measurement comes to the conclusion that difference in weight has nothing to do with difference in volume.

 

[wolfman]

I don't plan on sorting cases with this method. I'm just interested in checking case capacity for Quickload input.

 

[jlow]

I don't plan on sorting cases with this method. I'm just interested in checking case capacity for Quickload input.

In the end, regardless of why you measure volume, what you get back out from Quickload is only as good as the data you put into it. The old adage of garbage in garbage out applies here