Weighing cases acceptable variation?

Discussion in 'Reloading' started by encoreguy, Feb 24, 2008.

  1. encoreguy

    encoreguy Well-Known Member

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    When weighing cases how much total variation do you allow when you sort into your lots? +/- .5 grains for a total of 1 grain, or +/- 1 for a total of 2 grains, etc?
     
  2. Sludge

    Sludge Well-Known Member

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    Well, maybe im an anal nutjob, but I weigh mine and group them to within 0.1gr groups. I generally buy Nosler matched brass and that takes alot of work out of grouping them since they are already closely matched.
     

  3. Mikecr

    Mikecr Well-Known Member

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    There is simply no basis for it.

    If you really want to reduce ES from cartridge capacity variance, then measure precisely that. Check the H2O capacity of your fireformed cases.

    I know that weighing brass is easier than actually measuring. Just as weighing bullets is easier than measuring. Either might help you sleep, but both are a waste of time just the same.
     
  4. J E Custom

    J E Custom Well-Known Member

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    Encore

    When weighing for test they weigh the same.

    When weighing for hunting I stay within 1 gr.

    For long range hunting 1/2 gr.

    I normaly buy 200 rds at a time and weight sort and
    separate with this in mind.

    Anything that falls outside of these (Normaly I find 3 or 4 that
    are 2 or 3grs apart from all the rest) I use as dummys for die
    setup and COAL with different bullets.

    Just the way I do it
    J E CUSTOM
     
  5. Boss Hoss

    Boss Hoss Well-Known Member

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    Really it does not matter because you are not accomplishing anything as it relates to the volume of the case.
     
  6. Sludge

    Sludge Well-Known Member

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    Maybe I am completely ignorant, and I dont claim to be an expert, just a guy who has screwed around trying to find what worked and didnt work for him. However, how is there NOT a correlation between case capacity of a fireformed case and its weight? Say you have a batch of 100 new brass. If you fire form them through your rifle, you clean, trim and deprime them and then sort by weight, it seems that any deviation in weight must correspond to an internal volume change being that the cases are formed to your chamber and that the brass doesnt deviate in its density. Cruder than measuring with water? Perhaps, but it seems that it would be better than nothing. I started my long range persuit with Winchester brass several years back. The ES results on the chronograph as I have struggled over the years have shrunk. A big step in that was when I started matching brass. First I started culling from the winchester. Then later I got rid of the Winchester brass all together and switched up to the Nosler matched brass. Good results all around.

    Ive heard of using water, water and alcohol, using sand, fine powder, with primers in, out, puttied up, golf tees inserted in the flash holes, tape, ..... I know for internal ballistics programs they want water, but for a field shooter who is simply playing with a .300WinMag or something trying to reduce his ES why is weight sorting so wrong?

    Im not trying to flame anyone, just trying to understand why weight sorting as a means for determining a variance in volume for long range hunter not a wildcat experimenting with loads is so wrong. Please educate me with something other than ... "its meaningless"
     
  7. davewilson

    davewilson Well-Known Member

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    just take 10 cases that weigh exactly the same and then measure how much powder they hold. with my RUM case i've seen as much as 2 gr of powder difference with cases that weigh the same. i almost hate to agree with ole Boss because we usually argue enough to be married, but on this one we're on the same page.
     
  8. Boss Hoss

    Boss Hoss Well-Known Member

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    "MARRIED"????? Send me some MONEYThen ASAP !!!!! So little time so many guns to build!!!!!
     
  9. Boss Hoss

    Boss Hoss Well-Known Member

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    Sludge-----Sorry but I was just helping you to avoid wasting time. Anything you do with respect to weighing the entire case is meaningless with respect to the interior volume of the case. This means that you are making the assumption that by having 2 cases of the exact same weight that they have the identical internal volume. This is not a valid or logical assumption however; those two cases may just by happenstance have the same volume. Now we know that the internal volume of the case is what determines powder capacity and if the cases are different volumetrically, they will develop different pressure curves which will translate into different velocities. This will include among other things possible POI changes as well in addition when shooting at distances that are long enough the vertical dispersion caused by the different muzzle velocities will be very noticeable.


    If you in fact want to check the interior volume of your cases, then start with clean cases and fill each one with a powder that flows readily such as 748 to the top of the case and then weigh the charge. This takes more time plus you have to use water but fill each case with water (eye dropper or bulb syringe) and put a few drops of surfactant in the water (i.e. 1 gallon jug) to break the surface tension to ensure no voids (tiny bubbles) on the inside of the case. If you add surfactant or dishwashing soap, make sure you rinse them well when finished.


    Hope this helps.

    How did I do Dear and send MONEY???? LOL!!!!!!
     
  10. encoreguy

    encoreguy Well-Known Member

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    Well I guess I didn't get the response that I thought I would but that is how you learn. If you do the volume method, should you fireform first, clean and then what?
     
  11. Sludge

    Sludge Well-Known Member

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    Well, for some reason I still cant see how if the external dimensions are the same (fire formed, same length etc.) that with the same weight there can be a great volume difference... However, im gonna have to play with that now.

    2 gr of difference eh??

    Darn it Boss :p ya had to start me down the road to more experimentation...
     
  12. milanuk

    milanuk Well-Known Member

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    On the one hand... they are correct. The weight could be other places than just the case walls... like the extractor groove, or case head.

    On the other hand... people have done some tests in the past comparing weight and volume, and the results seemed to show (not 'prove') that for some brands... the weight did seem to be fairly
    indicative of the case volume in some instances, like Lapua .308 Win cases. Others, like Winchester .308 win... there was no correlation whatsoever.
     
  13. davewilson

    davewilson Well-Known Member

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    sorry Dear, i gave all of my money to my girlfriend!

    i think the main problem with weighing as a comparison is there can be areas of the metal which are more dense than others.the softer the metal, the more it is prone to differences in density.