SD question...

Discussion in 'ELR, Ballistics & Bullets Board' started by IdahoSharpshooter, Aug 3, 2017.

  1. Richard Coody

    Richard Coody Silver $$ Contributor

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    well for me SD is an indicator of the consistency of my reloading practices

    now that said what happens when a rifle is fired is a very complicated process. there are so many variables involved.

    barrels have numerous nodes. some are wide and forgiving and some are critically narrow. velocity and seating depth to name a few. you really have to let your target tell you what that barrel likes.

    in the reloading process you have

    accuracy of the powder charge. then you throw in the variables of primer, case volume and a few others.

    neck tension consistency and grip. variations in neck wall thickness ect....

    concentricity

    it is really a complicated process

    the further you shoot the more your inconsistencies will show up
     
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  2. gstaylorg

    gstaylorg Silver $$ Contributor

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    Sounds like you already had everything figured out before you even started this thread. Good luck with that.
     
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  3. IdahoSharpshooter

    IdahoSharpshooter Gold $$ Contributor

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    back to the question of what, if any, real world experience you have to back your posts...?
     
  4. damoncali

    damoncali Gold $$ Contributor

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    With all due respect, your understanding of what a distribution is (vs a sampling of a population with that distribution) is lacking. Look into that, and you'll find the answer to your questions.
     
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  5. IdahoSharpshooter

    IdahoSharpshooter Gold $$ Contributor

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    I base my assessment of multiple SD +/-'s and the bell curve VS a couple thousand rounds on target. I really would like to know, based on actual target results, what I am missing. Why do the targets MV and groups sizes not correspond to the %-age.

    Someone, anyone, please feel free to enlighten me...
     
    Last edited: Aug 8, 2017
  6. Richard Coody

    Richard Coody Silver $$ Contributor

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    so i would assume from your real world experience you would ignore SD and let the target tell you what the rifle likes.

    not a bad plan at all.

    to each his own
     
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  7. CharlieNC

    CharlieNC

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    Do your faster shots hit high, and the slow shots low on the target? How do these results compare to ballistic calculator at that range?
     
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  8. IdahoSharpshooter

    IdahoSharpshooter Gold $$ Contributor

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    it is difficult to assess, after the fact. I just saw no degradation over several years and the amount of rounds fired. I believe I will have to go to one of those electronic target camera systems to be able to record groups shot by shot to find the answer.

    Thanks to all who posted,

    Rich
     
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  9. savagedasher

    savagedasher Gold $$ Contributor

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    Thats part of the reason I think two shots works best . If one is off because of speed you can tell . Larry
     
  10. CharlieNC

    CharlieNC

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    Rich instead of shooting a group, use a target with multiple bulls eyes to shoot individually and you can tell whats going on.
     
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  11. Richard Coody

    Richard Coody Silver $$ Contributor

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    you can take colored sharpies and color each round a different color record the color and velocity of the round. when you look at the target the color will rub off on the paper. use white paper. i believe this will work for you
     
  12. ballisticdaddy

    ballisticdaddy Silver $$ Contributor

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    So over a period of several years you managed to load 3,100 projectiles from the same lot, 19 pounds +/- of powder from the same lot and 3,100 primers all from the same lot? What about the brass, was all that the same lot, case volume, weight and was it annealed after every load? Was every projectile the same exact length and weight? Where the atmospheric conditions always the same as well? These are all variables that could affect the target that have nothing to do with the alleged "SD" If your question was rhetorical then please disregard my comments.
     
  13. IdahoSharpshooter

    IdahoSharpshooter Gold $$ Contributor

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    I shot indoors. Speer used to sell DWM brass. I bought 500 cases, plus a box of twenty at Lolo Sporting Goods in Lewiston, ID. Lolo also used to buy all of Speer's cosmetic seconds bullets, and sell them by the pound. I did my load work with that twenty, annealed after each firing. Split a sleeve of 10,000 150gr MK's with two other guys. I bought 5000 Remington (Green and Orange boxes) of # 91/2 Bench Rest primers. They cost me $12 per K at the time. Sierra, at that time, used three separate point up dies, and just fed them all into one tub. Tumbled them, and put them in boxes of 100. My second year shooting HBR I was shown the difference in oal using the Sinclair hex nut comparator system. Two other shooters and I spent an entire weekend gauging them and sorting into separate piles, based on oal. +/- .001".
    I tend to buy things in bulk, two recent examples, I bought two 8lb jugs of RL-33 for my LM, and 500 new BELL cases when I decided to build a 404 Jefferys to hunt Africa with.

    I then loaded all 500 with the same load and shot them in HBR matches. I loaded them .020" into the lands, then seated each 100 ,020" off the lands. When all 500 had been fired, I annealed them and repeated the sequence.

    The data was gathered only on rounds fired in the seed warehouse. Temperature and humidity were controlled very carefully. If humidity is over a certain percent, seeds tend to sprout. Under, and they can shrivel inside and crack the hulls. Same for temperature. When you are growing flowers for the seeds, you control the harvested seed environment very carefully.
    Bullets sorted into .5gr lots, and loaded in that weight. DWM brass varied less than 2.5gr for the entire lot. LAPUA did not invent stringent QC, they merely refined it and made it a standard.

    This is not my first night rodeo. I bought my first 40X from Fred Sinclair for $240. I bought the Remington external scope at the same time. 24X, for $315.

    Are you gentlemen so married to the infallability and perfection of SD, that you cannot be open minded about a question? Everything in Litz's books (which are great in terms of the knowledge shared) shows little "." instead of round bullet holes on paper. He did not actually shoot 1000 rounds demonstrating how SD works, it is all theory. Based on the best answers to date, but still theory.

    What I want to know, and NObody seems to have an answer for, is why, the more rounds you fire, how one SD grows to two, and then to three SD's? How does an initial SD of 10 grow to SD of 20, and then 30. One, to two, to three SD's going from ten rounds to his calculated one-thousand, and the tremendous spread in theoretical group size...

    There is no consistency to a load that does that. I just want an explanation gentlemen.
     
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  14. Mozella

    Mozella

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    [QUOTE="IdahoSharpshooter, post: 37034550, member: 763606"........ snip.........
    Are you gentlemen so married to the infallability and perfection of SD, that you cannot be open minded about a question? ........ snip..................
    What I want to know, and NObody seems to have an answer for, is why, the more rounds you fire, how one SD grows to two, and then to three SD's? How does an initial SD of 10 grow to SD of 20, and then 30. One, to two, to three SD's going from ten rounds to his calculated one-thousand, and the tremendous spread in theoretical group size...

    There is no consistency to a load that does that. I just want an explanation gentlemen.[/QUOTE]

    It sounds like you have a good grasp on loading high quality ammo and testing it. However, you do not have a good grasp on what Standard Deviation is. It's not a theory any more than the number Pi is a theory. It's simply a tool used in statistics which describes the extent of the deviation within a group. Do some Googling for more information.

    Your last couple of paragraphs make no sense. It's like asking this question: "Your circle is larger than mine. Why is your Pi larger than my Pi. And why does Pi grow as we draw more and more circles? What's up with that?" The question shows a lack of understanding of what Pi means. Pi doesn't grow as you draw larger circles nor does sit change as you draw more circles; therefore, nobody can tell you why it does. No matter how often you ask the question, the answer will be the same. It just doesn't happen.

    You ask why one SD grows to two SD's and three SD's as you fire more rounds. The reason nobody can tell you why is because it doesn't happen.

    This is not the place for a lengthy lesson on what SD is (and what it isn't); however, the Internet is loaded with all the information you need to grasp the concept of what SD means.
     
  15. IdahoSharpshooter

    IdahoSharpshooter Gold $$ Contributor

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    I think it is time to let this one die.

    My apologies to anyone I have offended.

    Rich
     
  16. brians356

    brians356 Gold $$ Contributor

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    Here I always thought "SD" stood for "Savage Dasher". What the ... ? :confused:
    -
     
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  17. IdahoSharpshooter

    IdahoSharpshooter Gold $$ Contributor

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    For decades I thought is was the 421 CID Pontiac Super Duty racing motor.
     
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  18. brians356

    brians356 Gold $$ Contributor

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    Rich,

    If you're still listening: For small sample sizes (e.g. 5-shot string) and for our purposes (accuracy load development), SD probably has limited value, and in fact might even be misleading.

    Consider these two hypothetical 5-shot strings' muzzle velocities:

    String 1: 3100, 3195, 3190, 3205, 3200
    String 2: 3165, 3150, 3100, 3180, 3205

    Both strings have an ES of 105. But their population SDs are 39.3 and 35.0, respectively. That's not a large delta. But there's something which might be obvious (for such a small sample) by inspection - there is one "outlier" in String 1 (3100) - the other 4 samples (considered apart) have an extreme spread of only 15.

    One explanation for the String 1 outlier 3100 could be the first shot from a cold and/or clean barrel. Subjectively, we might well consider String 1 superior to String 2, even though they both have identical ES, and String 2 has a lower SD.
    -
     
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  19. IdahoSharpshooter

    IdahoSharpshooter Gold $$ Contributor

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    brians365,

    most helpful. Thank You!
     
  20. loudandproud

    loudandproud

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    If two rifles are exactly .250 MOA rifles at 100 yards, one has an SD of 4 and the other an SD of 20, the rifle with the 4fps SD WILL with ABSOLUTE certainty, make more impacts on target all other conditions being the same.

    Its not opinion, its physics and mathematics.
     
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