Do We Really Need To Know Metallurgy In Order To Get The Right Answer?

    This article insists throughout that people have to know metallurgy in order to understand the elemental data from the fragments in the JFK assassination. A typical quote: "An investigator cannot interpret the compositional analyses without regard to the realities of bullet production." The article then proceeds to use metallurgy and get the wrong answer. This may mean either that metallurgy is not essential, or that it just used the metallurgy wrongly. I think that both are true. The previous pages showed that the article jumped to a wrong conclusion from metallurgical reasoning. The next paragraphs show that one really does not need to know much, or maybe anything, about metallurgy in order to interpret the fragments properly.
    As an exercise, let us see how far we can go in interpreting the elemental data for the JFK fragments without appealing to metallurgy. First we can note that at the size of the smallest fragments, antimony is nearly homogeneous in the lead (heterogeneities of <6%, which is at the level of the analytical uncertainties). No surprises here. Next we can note that at the quarter-bullet scale, its heterogeneity has risen to 24%, well above the limit of detection. We then note that when we move upward to the bullet scale, its heterogeneities increase further, to 40% or 90%, depending on whether the base is three bullets or 14 bullets.
    There is an important feature here that is easy to miss. Since the 14-bullet results were derived from one sample per bullet, one might say that they do not represent anything larger than the quarter-bullet scale of the three bullets. In fact, that position cannot be excluded from the 14 points alone. But the quarter-bullet analyses give the lie to that idea—they clearly show that entire bullets can be high, medium, or low in antimony. Thus the size scale for heterogeneities in antimony extends to at least the size of whole bullets. Unfortunately, the available data cannot show whether it extends to greater sizes. If the data from the 14 bullets can be taken at face value, however, it would strongly appear that the heterogeneities go well beyond the size of individual bullets. That conclusion cannot yet be proven, however.
    Thus the bigger the sample of WCC/MC lead, the more it will differ in antimony from other samples of the same size. What are we to do with this difference? First, we can note that these differences can be dealt with statistically as long as they fit one of the well-known distributions. In the second Rahn-Sturdivan paper, Larry Sturdivan showed that they follow a log-normal distribution, which is the same distribution followed by the many lead samples considered in the 2004 NRC report. The only difference is a much bigger standard deviation for the WCC/MC leads. Second, we can go ahead and use the properties of this distribution to interpret the results, and in particular demonstrate the reality of the two obvious groups of JFK fragments. (See the Rahn-Sturdivan page here.)
    The much-bigger heterogeneity of MC lead is shown in the figure below (also from the first Rahn-Sturdivan paper), which compares within-bullet relative standard deviations (RSDs) of MC lead with several classes of bullets considered in the NRC report. Note how different the MC lead is.

    Notice how far we have come without having to know a thing about metallurgy. We have established that antimony in MC lead varies progressively more as the size of the fragments increase, that the variations follow a log-normal distribution, and that the variations are far larger than reported for other types of bullets. That is really all we have to know in order to properly interpret the data from the fragments—all without metallurgy.
    But we don't want to be complete ostriches and ignore metallurgy completely just because we can.
We can use it to take further steps. It is quite natural to wonder about the reasons for the large-scale heterogeneities in antimony. To get a general (operational) answer, we need know nothing more than that the Western Cartridge Company made MC lead by mixing scrap lead (some of which was rich in antimony because it came from other castings for hardened bullets) with virgin lead (very low in antimony), and that complete chemical homogenization was not necessary to meet the terms of the contract. Thus the final product was "clumpy" in antimony, and to a lesser extent in the other elements associated with the scrap material. It matters not whether you view the resulting vat as mixed like a marble cake, as I have opined in the past, or containing "nuggets" of high-antimony material, as Tony Marsh has suggested. The critical things are the scale of the heterogeneities and whether the resulting concentrations follow a reasonable statistical distribution.
    In other words, you don't really have to know about metallurgy to interpret the data properly, but it is nice to have a little for backup at the end.

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