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Thread: Weighing brass

  1. #1
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    Weighing brass

    Maybe interesting for some folks, old news for others... Someone at the club asked why people weigh brass and I looked up some figures to try to explain a little about the sense, or non-sense, for doing this (not just for BR, for plane-jane rec shooters as well).



    Brass = 8400 kg/m3

    Air = 1.29 kg/m3

    Vihta N133 = 870 kg/m3


    1 grain of brass displaces 1.29/8400 = 0.000153 grains of air

    1 grain of brass displaces 870/8400 = 0.965 grains of powder

    1 kernel of N133 weighs around 0.025grs

    So 1 grain in case weight gives the same result as 0.1gr of powder (in terms of volume, not weight), ie 3-4 kernels of N133.


    Depending on what you shoot (BR, plinking, high-power), that 0.1gr powder volume difference may mean nothing, or it may mean something. I can not, however (imho), see how sorting at the 0.1gr level of brass weight would mean anything, besides on paper, to real world results, as this would mean 0.01gr less volume for the powder.

  2. #2
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    VT52 when your shooting 1000 yards everything makes a difference, try weighing primers also, there can be a big difference. At 100- 200 not so much! Remember for every action there is a reaction in loading. One thing at a time so you know what done what.

    Joe Salt

  3. #3
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    I don't shoot BR at 1000, only F-Class. When I'm guessing to add or drop 2 minutes of wind I don't think 0.01grs case volume will make a difference to me . It all depends what game you are playing.

  4. #4
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    Another observation to add to the mix.
    Over the years, I used to start with 100 Lapua .30-06 cases to make a seasons worth of elk cartridges. As time went on, I noticed I had to start with 200 to make sure I could sort out about 80 "good ones".
    One of the drivers for sorting them in the first place was that when I checked the weights, I would always find samples that you could only describe as way out of family with the batch. (More than 4 sigma away from the average.)
    I used to keep them sorted out and marked them as fouling rounds. These cases were off the ends of the curve by more than 3 grains and were always found with wall thickness runouts above 0.002".

  5. #5
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    I shoot only point blank BR. If I shot with Joe Salt I'd crawl out 800 yards before firing. I will buy 1000 cases at a time whether I'm prepping for 6PPC or 30 BR. I wait for a sale and I pounce when I find one. I've been called a hoarder and I love it. During the long, cold, dark winter hours I turn the necks, trim to length, clean up pockets, and chamfer. Then I weigh the cases and separate them in 0.1 increments. I box them up in boxes of 100 cases. I now have enough cases to last me many years or so. As I see it, the problem with separating by weight is you don't know where the weight difference is. Is it in the body-shoulder-neck or is it in the case head? I figure it makes no difference if the fluctuation is in the casehead but I'm not taking any chances. It doesn't take all that long to weight segregate when you consider the investment of time in the prep work. Does it make a difference? I don't know but I'm taking care of one possible varient.

  6. #6
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    VT52

    I started competing in 1000 yard BR last year. So my methodology is to reduce verticle to the least amount possible. My first test was to shoot weight sorted brass to determine if I can reduce ES. My conclusion to the test is the weight of each case is a small percentage of ES. Powder type, primers, seating depth, ambient temperature and a host of other ever changing variables can wreck your day. I am with Joe S. and FBecigneul I want everything as perfect as I can make it.

    Eric K.

  7. #7
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    Would it not be more meaningful to measure inside case volume using water for this reason and measuring wall thickness for any deviation? Just weighing the brass and sorting by weight, when you don't know where that weight is, is kind of taking a lucky guess. I can imagine a case weighing the same but having a thin part and a bump somewhere where as the other case would be constant all around.

    Just trying to find out the real-world benefit of weighing cases to the extreme. The point not being that it is quick to do and having piece of mind, but if there is a real tangible effect at the 0.1gr level.

  8. #8
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    VT52
    I have been thinking about this for a while now. Being more of a tinkerer than an avid competitor
    I do not shoot competition point blank, only the odd club shoot, but i do have a range at home so that helps not having to drive across state.
    just making up 100 new lapua cases for my new 6PPC barrel
    What i am in the process of doing and am open to criticism here.
    sort by weight and mark the cases with marker pen
    neck turn to thickness .270" neck so .2675"
    polish neck with steel wool
    uniform primer pocket, check for burrs on the inside
    form a false shoulder and fireform in slave barrel with hornady butter, to give the best uniform lenght and reduce case stretch
    trim to lenght
    weigh again and batch into 0.5gn lots
    Have not got it completed so still keen to see any weight changes occur.
    JRB

  9. #9
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    kind of silly to weigh BEFORE brass prep.
    trim to lenght does not affect effective case volume( volume below the base of the bullet), but does affect weight
    neck turning does not affect case volume, but does affect weight.
    primer pocket uniforming does not affect case volume( you seat the primer to the bottom of the pocket), but does affect weight.
    now deburing the inner flash hole can affect case volume..but with lapua in 220 russian...very minor.

    so prep then sort

    you want one more sort.....???

    load them all the same..this requires a lab scale, because the "close enough" of a beam or thrown charge will not cut it.

    shoot in whatever string length you want..10 15.25....mark all cases that shoot OUTSIDE the mean group...use them for foulers......

    mike in co

  10. #10
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    That may work at short range, but at long-range I would end up with zero cases in a few trips to the range

  11. #11
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    lol...i agree...


    Quote Originally Posted by VT52 View Post
    That may work at short range, but at long-range I would end up with zero cases in a few trips to the range

  12. #12
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    Don't make this any more complicated or protracted than it has to be.

  13. #13
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    Mike, my 'madness' for weighing, before i started was to see if, in this case, if there was any changes in lots after the prep was completed.
    You must 'speculate' which promted this experiment for me, that removing material in varing amounts from case to case, and therefore weight must ultimately effect case volume if all cases are infact uniform in every way. Unless of corse the brass varies in quality or composition, which we can rule out with the top few brass manufacturers.
    My prevoius method has been as follows, happy for comment and advise
    New lapua brass get 'double' what you need than weigh into two groups to split the pack, put aside any with more than 1.5 grain difference from the group for foulers and setting up etc. Share with a mate or put away for later the other half.
    Do all the required prep than fire form and trim, work up a load and shoot
    I have tried the cull method as you explain but not been able to repeat the results, most probably because i do not understand the process and effect.

    I really like your method to cull brass, simple and effective for point blank shooting.
    Can you tell us more about the peramiters you use, and whether cases get a second chance etc?
    JRB
    Last edited by JRB; 01-14-2013 at 06:31 PM.

  14. #14
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    francis,
    the problem i see is the open comments...non br shooters...

    they are not using lapua or the like...
    they are using winchester and rem and they can infact benefit from weight sorting that stuff...


    mike in co

  15. #15
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    Ok, so what i am seeing, if i get it right.

    Top quality brass does not reqire any more sorting than just shoot it and cull?
    This really helps us guys, that cannot get to the big matches and learn more.
    If you guys are happy to share your brass culling method i am all ears.
    regards
    JRB

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