Case Volume Determination (pic heavy)

Discussion in 'Reloading Forum (All Calibers)' started by Ned Ludd, Feb 27, 2016.

  1. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    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, etc., each of which come with their own particular caveats and issues. For that reason, I thought I would share the method I use. It's simple, fast, precise, and requires only tap water, a couple paper towels, and an accurate instrument for measuring weight.

    The setup:

    [​IMG]


    2) Tare (zero) balance using fired case with the spent primer left in the pocket:

    [​IMG]

    3) In a small bowl with ordinary tap water, fill case near to full with case tilted slightly to prevent forming a bubble in the neck or case body:

    [​IMG]

    4) Place fingertip over neck opening and shake case down once or twice to get rid of any bubbles that may be inside:

    [​IMG]

    5) Wipe off the outside of the case with a paper towel, making sure to remove any water that may be in the extractor groove or at the edge of the primer.

    6) Check the meniscus (water surface) with a lamp or other light source slightly behind, which makes it very easy to see. The idea is to get the surface of the water as flat as possible. Some might take exception here, but this is a brass case, not a glass laboratory graduated cylinder where you can clearly see the bottom of the meniscus through the vessel. Moreover, the surface tension properties of water in a brass case are such that the surface is typically very flat when the case is correctly filled. I use a small drop of water on the tip of my finger to adjust the amount of water in the case:

    [​IMG]

    If the case is overfull, touching the [dry] tip of dry finger to the surface will pull a small amount of water out. A concave surface is underfilled, whereas a convex surface is overfilled (see images below). The backlighting makes it very easy to see when the surface is perfectly flat and the case is properly filled.

    [​IMG]
    Underfilled

    [​IMG]
    Overfilled

    [​IMG]
    Just right

    7) Weigh case and record measurement. If you use grams as the unit of weight, the conversion factor for grams to grains is to divide by 0.06479891 (or just 0.0648).

    As a demonstration of the precision of this method, I measured the case volume of a single piece of Black Hills .308 brass ten times, completely emptying out the water and re-measuring each time. Here are the results (weights in grams):

    [​IMG]

    As you can see the reproducibility of this method is very good, varying less than 0.02% (SD). If case volume translated directly to velocity, which it does not, this would represent a variation of ~ 0.6 fps for a load with 2850 fps muzzle velocity. In other words, well under what you can either measure or shoot. The limiting factor for this approach is obviously how well you can reproduce the "flat" meniscus. With only a very little practice, I think you'll find that backlighting makes it pretty easy to reproducibly fill the cases. So if you're interested in measuring case volume, give this approach a try. It's very easy, very fast, and very reproducible.
     
    Last edited: Feb 27, 2016
    Bc'z, RAD57, reubenski and 8 others like this.
  2. mao0720

    mao0720 Silver $$ Contributor

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    Great post greg. Do you do this with fired, unsized brass or resize then reseat a spent primer?
     
  3. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    As I mentioned above, for me this is typically used for fired brass to get a case volume for Quickload. I measure 10 fired cases selected at random, measure volume as described, and use the average [of 10] case volume as my Quickload value. But you can also pop a spent primer in a case to measure virgin brass, resized brass, whatever you want. I have done that a few times just to see how prepped virgin brass, fired brass, and fired/resized brass compared to one another in terms of case volume. In my hands with .308 brass, fired and fully resized brass was about halfway in between prepped virgin brass and fired brass.
     
  4. Marksman63

    Marksman63

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    Wow, 58.34gr!
    Large chamber and/or very thin case walls
     
  5. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    I think it's both. The Black Hills brass was fired from a DTA SRS rifle. Case volumes of Lapua brass from my competition rifles measured this way comes out to 55.5-55.7 gr, which is pretty consistent with what many others are getting.
     
  6. Sheldon N

    Sheldon N

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    Good stuff, thanks for sharing. Seeing the minimal variation in results and repeatability on the same case is encouraging.
     
  7. pemo

    pemo

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    Thanks for suggesting this method ! I tried it earlier today and got this result for some 243Win cases, fired, unsized, spent primer left in case.

    [​IMG]

    I have given a report in a separate thread "243Win: brass, brands, weights and velocities."

    Cheers,
    Pete
     
  8. Chappy

    Chappy

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    How consistent is a lot of Lapua brass been for you in the .308?
     
  9. Endyo

    Endyo

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    Great write up! This method by far is the easiest way to Volume weigh brass. It is a lot quicker than using a plug. Depending on how "accurate" you need your readings it can be a big time savings.

    I've found that actual volume may be slightly off due to carbon. This is probably not enough to matter for the purposes we plan on using the measuring.
     
  10. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    You're right, carbon particles can certainly be a problem with regard to overall accuracy in volume determination. For a small number of cases, it's pretty easy to rinse them with tap water a couple times prior to measuring volume. Most of the sizable pieces of carbon will come out. I don't worry too much about any traces that might remain.
     
  11. savagedasher

    savagedasher

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    Your only comparing volume of the case from one to the other . If they all have carbon and fired and un sized .
    Can't get any better than that. Larry
     

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