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308 v 7.62 case capacity

Discussion in 'Handloading and Reloading' started by chas442, Mar 18, 2017.

  1. Blue68f100

    Blue68f100 Member

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    There are several ways to get water volume. First the cartridge must be clean (inside and out) sized and deprimed. Now you need to seat the bullet to your OAL. Then invert bullet down in some holder so you can add water through the primer hole. This will be the exact volume that the powder has to work in. Doing it the easy way base down can give you some false reading since the neck lengths vary slightly.

    I've done it all 3 ways. The best is inverted, will give you the best results.
     
  2. ATLDave

    ATLDave Member

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    You said "So are you saying that facts and data don't matter."

    1. More data is derived from observations of the world outside of "controlled experiments." Data regarding the economy, weather, public health, crime rates.... all these are collected outside of controlled experiments. That causes challenges, but they certainly qualify as data.

    2. Even if data were only the quantified output of controlled experiments: What do you think shooting competitions are?

    Look, just argue that you have direct evidence of the lack of correlation between case weigh and case capacity (for at least cartridge), and that the other view is supported only by indirect evidence and/or evidence with confounding factors. Don't just say that facts and data aren't "facts and data."

    FWIW, I have no opinion whatsoever on the underlying matter. I don't know much about this topic. I found your information interesting.
     
  3. macgrumpy

    macgrumpy Member

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    Yes, and that was in answer to another post, that wasn't addressed toward you, you are the one that jumped in and started arguing about what was fact and what wasn't. My original comment was simply asking a question, I wanted clarification about where the poster stood on the factual data that I presented. Your responses seem to prove that my assumption was correct in that you at least don't believe that test data.

    While anecdotal evidence can be true it's still not data and data carries more weight when we are trying to find truth. The "fact" that shooters believe that weighing their cases is an accurate way to predict volume isn't true but it's still a fact that many believe in and they continue to use that process.

    If you want to prove anything then direct your energies toward the topic - Does weighing a case directly relate to the volume of the case? If you want to continue then provide some data that proves that I'm wrong. This bickering over semantics is just endless prattle.
     
    Last edited: Mar 20, 2017
  4. Walkalong

    Walkalong Moderator

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    No, I'm saying like doing it by weight, and that works really well for me, and others. I don't want to (Will not) go through the trouble doing it with water. YMMV. :)
     
  5. macgrumpy

    macgrumpy Member

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    I have no argument with that idea, as I said, for most shooters the water volume of a case isn't really important and I can understand that time is a big issue for most people.
     
  6. ATLDave

    ATLDave Member

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    mac', I'm just a bystander without a dog in the fight. I enjoy reading you and Bart and other knowledgeable folks talk about this topic. I would be particularly interested in how to reconcile two sets of data: 1. Your measurement data; and 2. the large volume of competition-derived data* that suggests that weighing cases is a very good way to sort them for high levels of precision and accuracy.

    Some possible explanations that I can imagine - I have no idea whether any of these are true:

    1. There's a difference in volume that isn't connected to weight, but it turns out that small differences in volume just don't matter at all.
    2. There's a difference in volume that isn't connected to weight, but it turns out that small differences in volume just don't practically matter, with other variables swamping whatever signal is there.
    3. The data from shooting competitions is different, in that many have been won with volume-sorted cases, and more so recently (no idea whether any part of that is true; if true, it would explain the difference).
    4. The particular cartridge chosen for the direct measurements you cite is somehow prone to large weight-volume disconnect, and common target-shooting cartridges lack this characteristic.
    5. The measurement data is bad.

    * Note that shooting competitions of they type referenced in this thread are generally scored quite objectively. How the shooters "felt" about their shots or their loads generally get no point value. Moreover, shooters are shooting under generally common conditions at calibrated lengths. Thus, they are experiments. They are measuring many factors, but among them are the precision and accuracy of the loads being used.
     
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  7. macgrumpy

    macgrumpy Member

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    I can easily reconcile the different two statements.

    1. One is scientific data and the other is simply an opinion based on unscientific observations by people that don't understand the difference.
    2. Most people build preconceived notions of what's true and what isn't and when their version of reality is challenged they simply reject any alternative proof out of hand.

    I'm not criticizing, I'm simply pointing out the truth of how we all think. Our brains always look for patterns that simplify things for us, we are looking for the simplest way to explain what we see. Most people relate weight to mass and they connect the idea of mass to shape and shape to volume; as a result, they quickly conclude that any shape change will change mass and volume but that's not true, the two are never directly related unless they are purposely controlled to achieve a specific weight or volume.

    The idea that since some competition shooters weigh their cases to control volume proves that it's true is a false conclusion, it only proves that some competition shooters think that weighing a case is a valid way to predict volume change, not that it actually does predict volume change. Without those competition shooters providing documented evidence that shows case weights directly reflect volumes we can only take their word for their perception that the two are related.

    The Flat Earth theory was still believed by some as late as the 1880s. One argument was that since the Nile river only falls a foot over 1,000 miles the ground was basically flat for that distance and therefore the Earth must be flat. At first blush this seems like a good argument, except that you could have a foot deep body of water on a large enough globe that you would never see the curvature of the globe. It's a great example of how limited personal experience controls how we think, if you never go more than 20 miles from your home then you could easily think that the world ends at the end of your vision. It also shows that a basic lack of knowledge can create misconceptions, the Nile falls far more than a foot, at least one waterfall is about 130 feet high.

    Here are the links to the information I posted about actual case weight and volume relationships
    Handloading...A Sorted Story

    Case Mass vs. Case Volume
     
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  8. ATLDave

    ATLDave Member

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    I think you are missing something pretty fundamental. We're not talking about hunters, where "good enough" is good enough. We're talking about people shooting with objective measurements as results.

    The fact that many competitive long-range shooters sort by weight isn't the proof... the fact that many competitive long range shooters are winning matches while sorting by weight is, in contrast, very significant. This is akin to one proof of the roundness of earth being that aircraft or nautical navigation that is done using a round earth model works very well. If the earth was flat, transoceanic flights and voyages plotted using a round earth model would land/arrive far off course. But they don't. And that's one way a layperson can easily know that the round-earth model is correct.

    Similarly, if sorting by weight wasn't a very good proxy for eliminating brass-driven variables in precision/accuracy, then shooters sorting by water volume would quickly start winning all the matches.

    Because that's what competition does and how it works. Performance is measured. Precisely because it is an experiment under relatively controlled conditions, the stuff that works wins, and the stuff that wins gets popular (because everybody else wants to win, too).

    So that still leaves the question of how to reconcile the two sets of data.
     
  9. Bart B.

    Bart B. Member

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    If a tiny spread in case volume is important for accuracy, what's its place on the component priority list for best accuracy?

    For example, consider this .308 Winchester load and the variables in its components loaded on two Dillon 1050 progressives:

    * New, unprepped Winchester cases; weight spread 3.5 grains, neck wall spread .0013". All as measured across 50.
    * Federal 210M primers.
    * 45.3 grains of IMR4895; charge weight spread .34 grains as measured across 50.
    * Sierra 155-grain bullet seated to 2.83 OAL average; weight spread .4 grains, bullet runout .0035" max.

    What's the best accuracy that should produce at 600 yards for a 20-shot test with all those big variables?
     
  10. Walkalong

    Walkalong Moderator

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    While it may be an opinion, it is based on experience and what winners do. It's a known fact many in the winners circle in different disciplines sort brass by weight, ergo, it's good enough. If someone was beating them all the time and the only thing they did differently was sort by water volume, everyone would change to that. Another "fact". If I shot a 6.789 MM and always won, guess what.... :)
     
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  11. Jim Watson

    Jim Watson Member

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    These charts showing a lack of close correspondence between case weight and case volume boggle my mind.
    I cannot see how containers of the same outside dimensions can vary in volume except by differences in the thickness of the container, and therefore its mass.
     
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  12. Bart B.

    Bart B. Member

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    Reminds me of when a friend won the 25 meter rapid fire pistol match in a 1960's Pan Am Games. People from other country teams were amazed at how small those 5-shot groups fired in 8, 6 then 4 second times were so well centered on the targets. Some of them asked if they could measure the exact location and diameters of the several holes in the under-barrel weight on that .22 short pistol he used. They got dial indicators and pin gauges getting numbers to 3 or 4 decimal places.

    He and the rest of the USA Team knew the pistol smith who rebuilt that pistol just randomly drilled those holes with whatever drill was at hand until its weight balanced the arm as desired by its shooter. They kept quiet and let the people have their way measuring things that didn't matter. None of them wanted to weigh that ugly looking hunk of rusty steel.
     
  13. ATLDave

    ATLDave Member

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    And after a couple of years when it turned out the shape of those holes wasn't the "secret sauce," I bet they quit trying to duplicate that method, didn't they?
     
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  14. RugerOldArmy

    RugerOldArmy Member

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    Well, it would make sense if the cases are constructed differently, like these:

    [​IMG]
     
  15. Jim Watson

    Jim Watson Member

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    I bet the UMC weighs less and holds more.
     
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  16. Walkalong

    Walkalong Moderator

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    No doubt.
     
  17. RugerOldArmy

    RugerOldArmy Member

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    I'm thinking the same thing Jim.
     
  18. RugerOldArmy

    RugerOldArmy Member

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    Personally, I think macgrumpy had a valid and interesting point, with his article.

    Simply consider two cases, identical in weight, amount of brass making them up, but one with a longer neck, or another with the shoulder pushed back, and you could see macgrumpy's point.

    All things being equal, weight should work fine.

    Yet as we all know with handloading, consistency is a hurdle, and identical pieces of brass are a hard fought goal.

    Imagine two pieces of brass, totally identical, but you take one and chamfer/debur it. It would be lighter, but hold no more.

    In terms of accuracy, I think this is overblown, however. Perfectly similar bullets would be much higher on my list. I'd be sorting the bullets by weight, diameter, and ogive, before I sorted the cases by weight.

    I think runout of a loaded cartridge would be more important than the minor capacity differences as well.
     
    Last edited: Mar 20, 2017
  19. Bart B.

    Bart B. Member

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    Neither link's standard was having all cases in a full length sizing die so their outside dimensions would be most consistent. Fired case outside dimensions have greater spreads and shapes than full length sizing die chambers do.
     
  20. macgrumpy

    macgrumpy Member

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    When one of you actually does a test of your own and proves that weight and volume are directly related then we might actually get somewhere but until then you're just wasting everybody's time.
     
  21. RugerOldArmy

    RugerOldArmy Member

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    Even after full length sizing, you would still potentially have trim length variances too...which bolsters macgrumpy's point. All things equal, the volume could be the same, and the weight differ.

    People have a tendency to see only the data that reinforces their bias.
     
  22. Jim Watson

    Jim Watson Member

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    There was a benchrest shooter who did a final sort.
    After all the usual brass prep, he then discarded any case that gave an uncalled wide shot. Groups improved.
     
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  23. RugerOldArmy

    RugerOldArmy Member

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    Interesting approach. Rather than eliminate all the potential causes, (or after doing his best), he sorted by effect.

    Maybe we can all learn from him. He was thinking outside the box.

    A lot of the fun in shooting, is improving our results, anyway we can. I admire his ingenuity and dedication. Ruthless. I bet he was a solid competitor.
     
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  24. Walkalong

    Walkalong Moderator

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    Some would save those and use them for fouling shots, but would never use them for the group. It's better to just toss them though. The only tough part is being sure it is the case. One odd shot a bad case doesn't make. It has to be a pattern. Same for seating. After painstakingly prepping cases for a tight necked chamber, if the seating pressure felt different on one you set it aside for a fouler. If it did it twice, it was scrapped.
     
  25. Load Master

    Load Master Member

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    First and foremost (at least to me) this thread is a fun read and I appreciate the thought that everyone has put into it. What would be fantastic is a chart that shows influence for given round component and or attribute. For example 2% change in powder weight has a larger affect on point of impact compared to 2% change in case volume. This chart would show what feature has the biggest change to point of impact at the target.

    What I'm suggesting, maybe volume doesn't really matter, to a point. The bottom line, at least for me, is placement down range on a target as repeatable as possible. This is my goal. However I have many things that affect my ability to accomplish this. The features I know will change point of impact that mathematically are ease to prove include:
    • Bullet mass
    • Bullet coefficient of friction
    • Bullet velocity
    Other features that have an affect on point of impact that might be more difficult to calculate includes:
    • Shooter influence
    • Atmospheric conditions
    • Gun variables
    My point, there are many variables that ultimately affect the point of impact on a target down range. In my opinion spending a lot of time on small differences in case volume is a waste of time. It would be better spent on repeatable powder drop, same mass bullets, consistency in round assembly etc...

    Thinking about what happens when I pull the trigger, the point that the primer ignites the powder and the pressure in the case rise, the case will inflate until constrained by the chamber walls. So the small difference in case volume will change almost instantaneously to fit the chamber when the round is fired. It is just my opinion, but the small difference in case volume before pulling the trigger I believe would have very little affect on bullet point of impact compared to all the other variables. Just my two cents worth on a complex issue.
     
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