Lack Of Supporting Data

    You would think that a metallurgist would leap at the chance to provide abundant supporting data for his metallurgical argument, and yet such is not the case in this article. There are several obvious places where hard data are required to complete the argument, but little or nothing is offered.
    The most striking omission forms a gaping hole in the central metallurgical argument, namely that the grain-size variations in copper and antimony control their fragment-size variations, and so remove any sense of special properties from the WCC/MC lead. Here the argument needs hard data to move from qualitative to quantitative. It needs to prove quantitatively that the first one (differences in concentrations at boundaries vs. centers) actually controls the second one (variations of copper and antimony in actual fragments). The beginning of the article says they do, the end of the article says they do, but does middle prove these claims?
    No, it doesn't prove it, or even come close to proving it. It does not give actual concentrations of antimony at grain boundaries of WCC/MC lead, or even how enriched they might be relative to grain centers. It does say, however, that "Such segregation could easily result in large relative differences in local antimony content." I think we can all agree that "could" and "large relative differences" are too vague to have any real import here, however. It then follows up this statement with "Segregation, such as that shown in Fig. 3, could easily cause local variations in antimony content of ± 100–200 ppmw [by weight] in the 50-mg MC material." Where is the quantitative backup for this statement? There is none in the paper. Without backup, it is a wish rather than anything scientific. The 100–200-ppm variations that grain-size variations can "easily produce" are essentially the same as the 300-ppm variations cited from Guinn's measurements. This is presented as the end of the story as far as WCC/MC leads are concerned.
    The argument for variations of copper goes the same way. It first says: "We would therefore expect copper to segregate as a separate phase at the boundaries and/or form grain-boundary atmospheres in soft leads … ," and it shows precipitated copper at grain boundaries in Figure 4. But if you are looking for any calculations, or even estimations, of how much this might affect the copper in actual samples, you won't find it, or any reference to it, in this paper.
    Thus the logic for antimony and copper is the same—they vary in crystals and they vary in fragments, so the two must be cause and effect. Why must they be cause and effect? Simply because the article says so, not because of any backup, because it offers none.
    Other parts of the metallurgical story also lack supporting data or appear to be influenced by misleading use of data. A good example is the section on grain size vs. fragment size. It
notes that typical grain sizes in WCC/MC lead are 500–1000 µm, but that is hard for most people to get a feeling for. Much easier is to express it as 0.5–1.0 mm. But that is the same as the reported size of WCC/MC samples and crime scene fragments (0.5–1.0 mm in dimension). That would make it easy for the fragments to fit inside one or two crystals and consequently to vary strongly in copper and antimony, depending on the proportions of boundary vs. center that composed them. But it doesn't happen that way. As seen in the next section, the copper hardly varies relative to the antimony, except for a small number of erratic outliers.
     The stated size for the grains, 0.5–1.0 mm, also appears to be misleading. Since the diameter of an MC bullet is 6.5 mm, there should be only 7–13 grains across the end of a bullet. But the article's Figure 5 (grain structures for three thin sections of an MC bullet) tells a different story. Lines drawn across the middle of those cross-sections intersect 30 fragments, 23 fragments, and 14 fragments in sections a through c, respectively (from the upper picture to the lower picture). Thus all three cross-sections have significantly more grains than expected from the article. Only the lowest one comes close to its projections, and it is right at their high end. These measurements mean that it is easier for fragments to represent more crystals of lead than the article leads us to believe. This conclusion agrees with the lack of correlation between copper and antimony described for the sets of samples in the next section. It is yet another indication that these theoretical arguments about the effect of grain size on the JFK fragments are wrong.

    The article also strongly implies that WCC/MC lead is no different from any other soft lead. The only data it offers in support of this claim is a statement that the ranges of copper and antimony in WCC/MC lead "are quite similar to other commercial FMJ bullets." That might well be, but ranges are very general properties, and do not necessarily capture differences among the leads such as standard deviations and physical scales of variation. The standard deviations of WCC/MC lead do indeed appear to differ considerably from other leads, as demonstrated by comparing Guinn's data with data from the NRC's recent report Forensic Analysis: Weighing Bullet Lead Evidence. For example, intrabullet and interbullet differences of most elements in most leads are typically <5%, in great contrast to the 24% and 90% for antimony measured in WCC/MC lead. In other words, WCC/MC lead differs qualitatively from the many leads of the NRC report.
    The physical scales of variation of antimony in WCC/MC lead are treated in the sections "Failed Prediction About Variability Vs. Size of Fragments" and  "Do We Really Need To Know Metallurgy?" They are larger than this article's metallurgical theory allows for.
    Thus the article is presenting theoretical, incomplete arguments about the supposed effect of metallurgy on the fragments when actual data on the subject prove it wrong.

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