Chiang Mai Med J 2007;46(2):75-82.

Original article

COMPOSITION OF METALS ON DIFFERENT TYPES OF FIRED BULLETS Piya Durongkadech, M.D., Karnda Vichairat, M.D., Pongruk Sribandidmongkol, M.D., Klintean Wunnapuk, M.S. Department of Forensic Medicine, Faculty of Medicine, Chiang Mai University

Abstract To ascertain how metals on the surface of shot bullets refer to the type of bullets, 12 lead bullets, 13 full metal jacket bullets and 18 semi-jacketed bullets were drawn from gunshot victims. Lead, copper, zinc and nickel, including the proportion of lead and copper were measured from the retained bullets to determine the relationship between these metals and types of bullets by using atomic absorption spectrophotometer to determine. There was not much zinc and nickel detected on all three bullet types, whereas a lot of lead and copper was evident. Though lead and copper levels were significantly different among the three types of bullets, and only their proportion might be useful for distinguishing them from each other. Chiang Mai Med J 2007;46(2):75-82. Keywords: metal, bullet

Death from firearms is still an important problem in many countries including Thailand. Sixteen to nineteen percent of the population in the United State own handguns.(1-3) During 1988-1997, 68% of 233,251 homicide victims in the United States were shot to death, of which, the majority was by a handgun.(4) Death from gunshot injuries has been considerable in northern Thailand. It was 8.9% of the total autopsy cases at the Department of Forensic Medicine between 2000 and 2005. About 85% of them were homicide. Handguns, especially revolvers and semi-automatic pistols, are commonly used. Because of the difference in

their muzzle velocity, different types of bullets are used. The muzzle velocity of a revolver is about 500 ft/sec, whereas the velocity of a semi-automatic is 1,000-1,200 ft/sec.(5) The higher the velocity, the more heat is produced. Therefore, the types of bullets used for semiautomatic pistols has to endure more heat than those used for revolvers. Many kinds of metal are used to produce bullets. Lead is commonly used because of its high density and kinetic energy. However, it has a low melting point compared to other metals. As a result, it leaves deposits inside the bore of a handgun if the muzzle velocity is

Address requests for reprints: Karnda Vichairat, M.D., Department of Forensic, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand. E-mail:[email protected] Received 23 April, and in revised form 28 May 2007.

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greater than 1,000 ft/sec and may cause a bullet to jam.(6) For this reason, lead bullets are only used for revolvers that have lower muzzle velocity.(7) Since semi-automatic pistols have a higher muzzle velocity, the lead core of bullets has to be covered with hard-to-melt metals. Copper, cupronickel (copper and nickel) or steel are widely used for this purpose.(6) A bullet that is completely covered with a hard metal sheath is called a full metal jacket bullet. If the tip of jacketed bullet is left uncovered, thus helping expansion inside the victim’s body, it is called a semi-jacketed bullet.(7,8) Each type of bullets from different manufacturers contains various kinds and levels of metals. In this study, we identified and measured the levels of 4 metals, which were lead (Pb), copper (Cu), zinc (Zn) and nickel (Ni), on the surface of lead bullets, semi-jacketed bullets and full metal jacket bullets. Besides, the proportion of lead and copper was analyzed to see whether it was different among these bullet types. We hypothesized that the levels of these four kinds of metal and proportion of lead/ copper in each type of bullet might be unique. Material and method This study was approved by the Research Ethic Committee, Faculty of Medicine, Chiang Mai University on April 20, 2006. Forty three bullets were removed from the bodies of victims who were shot to death by handguns between September 2005 and September 2006. All victims died before or on admission to Maharaj Nakorn Chiang Mai University Hospital. The autopsies were conducted at the Department of Forensic Medicine, Faculty of Medicine, Chiang Mai University. After the bullets were taken from the corpses during autopsy, they were cleaned with

Duronkadech P, et al.

sterile normal saline and dried at room temperature. Each bullet was wiped with a swab soaked in 5% nitric acid solution. The swab was then put in a glass tube filled with 5% nitric acid solution and left overnight at room temperature to dissolve the metal elements into the solution. Then, 0.1% nitric acid was added into each tube to make a volume of 10 mL. All of the samples were stored at -20 °C in a refrigerator for further laboratory analysis. The determination of Pb, Cu and Ni was carried out by a Graphite furnace atomic absorption spectrometer-Zeeman background correction Model Varian spectrAA800, equipped with a GTA-100 graphite tube atomizer. The tubes were coated with pyrolytic graphite (Varian, Australia). Pb, Cu and Ni hollow cathode lamps were operated. Argon was used as a purge gas delivered at a 300 mL/min flow rate (stop-flow during atomization). Zeeman background correction was applied. The conditions of the instrument and temperature program were validated in our laboratory. The wavelength for Pb, Cu and Ni were 283.3, 327.4 and 232.0 nm, respectively. Zinc determination was performed on a Perkin Elmer Model 3110 Flame atomic absorption spectrometer, equipped with a Zn hollow cathode lamp and deuterium lamp for background correction, at a respective resonance line using an air-acetylene flame. The oxidant and fuel flow rate were 10 L/min and 2 L/min, respectively. The methods for these metal measurements were validated. The results are shown in Table 1. The linearity for Pb, Cu, Ni and Zn standard was checked in the concentration range of 30-1000 mg/L. The calibration curves were obtained from standard at five different concentrations, with triplicate determinations for each point. Response linearity in the analysis

Composition of metals on fired bullets

was verified for the concentration ranges used in the experiments, and correlation coefficients were found to be 0.9980, 0.9995, 0.9978 and 0.9994 for Pb, Cu, Ni and Zn, respectively. The limit of detection (LOD) and the limit of quantitation (LOQ) in the acid digest were set at three and ten times the standard deviation of the reagent blank, respectively. The LOD was found to be 2 mg/L for Pb, Cu and Ni, and 25 mg/L for Zn. The LOQ was found to be 5 mg/L for Pb, Cu and Ni and 60 mg/L for Zn. The control samples were used to determine the precision of the method. The precision of a quantitative method was the degree of agreement among individual test results when the procedure was applied repeatedly to multiple sampling. It was measured by repeatedly injecting a standard concentration and calculating coefficient of variation of the results within a single run (intra-assay) and

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between different assays (inter-assay). The instrument precision was calculated from ten measurements of 10, 50 and 80 mg/L of Pb, Cu and Ni standard solutions and 100 and 500 mg/L of Zn standard solutions. The result of this validation method is shown in Table 1. Statistical analysis The mean, standard error of mean (SEM) and 95% Confidential Interval (CI) of all metals were calculated according to bullet types. Differences in the mean of metal level between the three groups were compared using the Kruskal-Wallis test and MannWhitney U-test. Statistical analysis was carried out using SPSS for Windows (Version 14.0). Results Forty three bullets were classified by their metal sheath into 3 groups; lead bullets (LB),

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semi-jacketed bullets (SB) and full metal jacket bullets (FJ). Twelve bullets were LB, 13 were FJ and 18 were SJ. The elements of Pb, Cu, Zn and Ni, were detected in all three groups of bullets (Table 2). The mean (± SEM) level of Pb in LB was 35,621.25±4,832.27 µg/L, which was higher than the level in SJ and FJ. The level of Pb was significantly different among each type and each pair of bullets (p