https://www.kenrahn.com/JFK/Scientific_topics/NAA/NAA_and_assassination_II/Guinns_NAA.htmlGuinn’s results for silver and antimony are shown in Table 15.[3] Two features of these data should be understood clearly: only single fragments are reported; and the uncertainties refer to only the counting procedure, not to other aspects of the measurement process or to variations within a specimen. Full uncertainties of measurement will be roughly twice as high, and variations within a specimen are several times higher than counting uncertainties. The sole exception is Q14, where both fragments listed in Table 14 were analyzed for Table 15. Thus the uncertainty for Q14 represents heterogeneities in the sample, as well as counting uncertainties. Q5, the smaller fragment from the President’s head, with a mass of only 5.4 milligrams, was analyzed but not reported. The smaller piece of Q9, fragments from the Governor’s wrist, had a mass of only 1.3 milligrams and was also analyzed but not reported. Thus for all intents and purposes, Guinn’s results are for single samples.
Guinn’s results are very similar to those of the FBI 13 years earlier. Data for silver are almost identical, and will not be discussed further because they do not differ much from fragment to fragment. Guinn’s data for antimony agree well with the FBI’s Run 4, as seen in Figure 9. No error bars are shown here because they are discussed in detail in the section on heterogeneity of antimony. Thus, Guinn and the FBI produced nearly identical results for the fragments, even though different pieces were analyzed.
Guinn’s conclusions
Guinn reached three key conclusions from his results, as reported in his Analytical Chemistry paper: (1) to a “high probability,” the fragments all came from Mannlicher-Carcano bullets; (2) there was positive evidence for two and only two bullets; and (3) the results grouped in a way that supported the single-bullet theory. The next sections discuss these results separately.
The fragments are all from WCC/MC bullets
The full statement of this result is that antimony in all the bullet fragments is “in the unusual (though not necessarily unique) concentration ranges of WCC/MC bullet-lead samples.”[4] This made it highly probable that they actually were Mannlicher-Carcanos. It is highly unlikely that any of the fragments came from any other kind of ammunition.
The justification for these conclusions comes for Guinn’s analyses of many different kinds of ammunition. As early as July 1971, Guinn had reported the concentrations of antimony and various other trace elements in 36 kinds of ammunition.[5] Although Mannlicher-Carcano ammunition was not tested here, three lots of 0.38-caliber bullets from Western Cartridge Company were.
Already by 1971, Guinn had focused on antimony as the principal indicator element in bullet lead. The reason antimony was so useful was that it was added to some leads up to 4% or so as a hardening agent. This made its concentration range from 10 or 20 ppm un virgin lead to 40,000 ppm in hardened lead, a much larger range than for elements that were not added to the lad. Guinn listed the concentrations of antimony in each of the 36 lots of bullets. He also listed the concentrations of 1–3 other elements if he was able to measure them. The 36 concentrations of antimony are shown in Figure 10.[6] A logarithmic scale had to be used for antimony because its concentrations ranged over nearly four orders of magnitude.
The range of antimony in Mannlicher-Carcano bullets reported by Guinn, 20–1200 ppm, is also shown, for comparison. It corresponds almost exactly to a group of seven bullets that is below the other 29 by nearly an order of magnitude. (The cause of the two distinct groups is probably just hardened lead versus unhardened lead in the bullets. By contrast, Guinn found that silver varied much less in concentration in the suite of bullets—two orders of magnitude vs. the four for antimony. The reason is probably just that silver is not deliberately added to bullets. Guinn also found that the concentration of silver in Mannlicher-Carcano bullets falls in the middle of the range of concentrations for other types of bullets (Figure 11). The reason for this is also presumably that silver is not added to lead the way antimony is.
The fragments from the assassination can be treated in the same way (Figure 13). Here, however, the ranges of concentration are much smaller. The predicted occurrence of false positives would be (2/19)(2/19) = 1.1%, or 0.2 bullets. The actual occurrence is is no bullets (0%), which is not surprising in view of the 0.2 bullets predicted above. But this is not the right calculation, which must be the fraction of non-MC bullets falling within the area of the fragments divided by the fraction of MC bullets falling within the same area. [The earlier calculation for MC bullets as a whole was a special case of this more general one, where the denominator was 100% (of the MC bullets falling within the MC area).] Since the fraction of MC bullets falling within the range of the assassination fragments is (1/12)(7/12) = 4.9%, the true percentage of false positives becomes [(2/19)(2/19)]/[(1/12)(7/12)], or 22.8%. This latter figure should be regarded as a very rough one because of the small number of cases that went into calculating it. To see just how rough it is, one need only note that no bullets of either kind fell within the narrow zone of assassination fragments. It is probably better then to revert to the earlier calculation for MC bullets as a whole, with a 5%–10% probability of being some other kind of bullet. This assessment agrees with Guinn's characterization of “highly unlikely.” It is also agrees with his statement in Analytical Chemistry that his results “have demonstrated that, to a high degree of probability, all of the bullet-lead evidence specimens are of WCC/MC 6.5-mm brand…”
