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

Address requests for reprints: Karnda Vichairat, M.D., Department of Forensic, Faculty of Medicine, Chiang MaiUniversity, Chiang Mai 50200, Thailand. E-mail:kvichair@mail.med.cmu.ac.th

Received 23 April, and in revised form 28 May 2007.

Original article

COMPOSITION OF METALS ON DIFFERENT TYPESOF 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 fromgunshot victims. Lead, copper, zinc and nickel, including the proportion of lead and copperwere measured from the retained bullets to determine the relationship between these metalsand types of bullets by using atomic absorption spectrophotometer to determine. Therewas not much zinc and nickel detected on all three bullet types, whereas a lot of lead andcopper was evident. Though lead and copper levels were significantly different among thethree types of bullets, and only their proportion might be useful for distinguishing themfrom each other. Chiang Mai Med J 2007;46(2):75-82.

Keywords: metal, bullet

Death from firearms is still an importantproblem in many countries including Thailand.Sixteen to nineteen percent of the populationin the United State own handguns.(1-3) During1988-1997, 68% of 233,251 homicide victimsin the United States were shot to death, ofwhich, the majority was by a handgun.(4) Deathfrom gunshot injuries has been considerable innorthern Thailand. It was 8.9% of the totalautopsy cases at the Department of ForensicMedicine between 2000 and 2005. About 85%of them were homicide. Handguns, especiallyrevolvers and semi-automatic pistols, arecommonly used. Because of the difference in

their muzzle velocity, different types of bulletsare used. The muzzle velocity of a revolver isabout 500 ft/sec, whereas the velocity of asemi-automatic is 1,000-1,200 ft/sec.(5) Thehigher the velocity, the more heat is produced.Therefore, the types of bullets used for semi-automatic pistols has to endure more heat thanthose used for revolvers.

Many kinds of metal are used to producebullets. Lead is commonly used because of itshigh density and kinetic energy. However, ithas a low melting point compared to othermetals. As a result, it leaves deposits insidethe bore of a handgun if the muzzle velocity is

76 Duronkadech P, et al.

greater than 1,000 ft/sec and may cause a bul-let to jam.(6) For this reason, lead bullets areonly used for revolvers that have lower muzzlevelocity.(7) Since semi-automatic pistols havea higher muzzle velocity, the lead core ofbullets has to be covered with hard-to-melt met-als. Copper, cupronickel (copper and nickel)or steel are widely used for this purpose.(6) Abullet that is completely covered with a hardmetal 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 typeof bullets from different manufacturerscontains various kinds and levels of metals.

In this study, we identified and measuredthe levels of 4 metals, which were lead (Pb),copper (Cu), zinc (Zn) and nickel (Ni), on thesurface of lead bullets, semi-jacketed bulletsand full metal jacket bullets. Besides, theproportion of lead and copper was analyzed tosee whether it was different among these bullettypes. We hypothesized that the levels of thesefour kinds of metal and proportion of lead/copper in each type of bullet might be unique.

Material and methodThis study was approved by the Research

Ethic Committee, Faculty of Medicine, ChiangMai University on April 20, 2006.

Forty three bullets were removed from thebodies of victims who were shot to death byhandguns between September 2005 and Sep-tember 2006. All victims died before or onadmission to Maharaj Nakorn Chiang MaiUniversity Hospital. The autopsies wereconducted at the Department of ForensicMedicine, Faculty of Medicine, Chiang MaiUniversity.

After the bullets were taken from thecorpses during autopsy, they were cleaned with

sterile normal saline and dried at room tem-perature. Each bullet was wiped with a swabsoaked in 5% nitric acid solution. The swabwas then put in a glass tube filled with 5%nitric acid solution and left overnight at roomtemperature to dissolve the metal elements intothe solution. Then, 0.1% nitric acid was addedinto each tube to make a volume of 10 mL.All of the samples were stored at -20 °C in arefrigerator for further laboratory analysis.

The determination of Pb, Cu and Ni wascarried out by a Graphite furnace atomicabsorption spectrometer-Zeeman backgroundcorrection Model Varian spectrAA800,equipped with a GTA-100 graphite tube atom-izer. The tubes were coated with pyrolyticgraphite (Varian, Australia). Pb, Cu and Nihollow cathode lamps were operated. Argonwas used as a purge gas delivered at a 300mL/min flow rate (stop-flow during atomiza-tion). Zeeman background correction wasapplied. The conditions of the instrument andtemperature program were validated in ourlaboratory. The wavelength for Pb, Cu and Niwere 283.3, 327.4 and 232.0 nm, respectively.

Zinc determination was performed on aPerkin Elmer Model 3110 Flame atomicabsorption spectrometer, equipped with a Znhollow cathode lamp and deuterium lamp forbackground correction, at a respective reso-nance line using an air-acetylene flame. Theoxidant and fuel flow rate were 10 L/min and2 L/min, respectively.

The methods for these metal measurementswere validated. The results are shown in Table1. The linearity for Pb, Cu, Ni and Zn standardwas checked in the concentration range of30-1000 mg/L. The calibration curves wereobtained from standard at five different con-centrations, with triplicate determinations foreach point. Response linearity in the analysis

Composition of metals on fired bullets 77

was verified for the concentration ranges usedin the experiments, and correlation coefficientswere found to be 0.9980, 0.9995, 0.9978 and0.9994 for Pb, Cu, Ni and Zn, respectively.

The limit of detection (LOD) and the limitof quantitation (LOQ) in the acid digest wereset at three and ten times the standard devia-tion of the reagent blank, respectively. The LODwas found to be 2 mg/L for Pb, Cu and Ni, and25 mg/L for Zn. The LOQ was found to be 5mg/L for Pb, Cu and Ni and 60 mg/L for Zn.

The control samples were used to deter-mine the precision of the method. The preci-sion of a quantitative method was the degreeof agreement among individual test resultswhen the procedure was applied repeatedly tomultiple sampling. It was measured by repeat-edly injecting a standard concentration andcalculating coefficient of variation of theresults within a single run (intra-assay) and

between different assays (inter-assay). Theinstrument precision was calculated from tenmeasurements of 10, 50 and 80 mg/L of Pb,Cu and Ni standard solutions and 100 and 500mg/L of Zn standard solutions. The result ofthis validation method is shown in Table 1.

Statistical analysisThe mean, standard error of mean (SEM)

and 95% Confidential Interval (CI) of allmetals were calculated according to bullettypes. Differences in the mean of metal levelbetween the three groups were comparedusing the Kruskal-Wallis test and Mann-Whitney U-test. Statistical analysis was carriedout using SPSS for Windows (Version 14.0).

ResultsForty three bullets were classified by their

metal sheath into 3 groups; lead bullets (LB),

78 Duronkadech P, et al.

semi-jacketed bullets (SB) and full metal jacketbullets (FJ). Twelve bullets were LB, 13 wereFJ and 18 were SJ. The elements of Pb, Cu,Zn and Ni, were detected in all three groupsof bullets (Table 2). The mean (± SEM) levelof 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 differentamong each type and each pair of bullets(p<0.01). The level of Cu was highest in FJ at1,301.70±608.35 µg/L, and lowest in LB at39.14±24.84 µg/L. There was a significantlydifferent Cu level among the three bullet types(p<0.01). After testing each pair, a significantdifference was found in LB when comparedto FJ and SJ (p<0.05). There was no differ-ence between the Cu in FJ when compared tothat in SJ. The concentration ratio of lead andcopper (Pb/Cu) was also significantly differ-ent among the types of bullets (p<0.01) andevery pair in each bullet group. The levels ofZn were detected in all bullet types, but therewas no significant difference among groups(p=0.93). All three types of bullets containedlow levels of Ni, which were 3.90±0.936 µg/L,3.92±0.86 µg/L and 10.19±2.86 µg/L in LB, FJand SJ, respectively. The level of Ni detectedin all bullet types was not significantly differ-ent (p=0.11).

While the mean of each group was differ-ent, the CI showed distinction between eachtype of bullet. The 95% CI of each metal andPb/Cu ratio are shown in Table2. The 95% CIof Pb/Cu ratio for LB was between 1,314.12and 4,090.62, which was significantly higherthan for FJ (between -1.43 and 7.13) and SJ(between 94.61 and 584.75). This ratio exclu-sively distinguished all three groups of bullets(Fig. 1). Meanwhile, the 95% CI of Pb alonewas able to distinguish only FJ from LB andSJ, but not LB from SJ (Fig. 2). On the other

Composition of metals on fired bullets 79

hand, as shown in Figure 3, Cu levels of allthree types of bullets overlapped.

DiscussionFrom the experiment, we demonstrated that

Pb, Cu, Zn and Ni were detected from all threebullet types, which were LB, SJ and FJ. It has

Figure 1. 95%CI of Pb/Cu in different bullet types.

Figure 2. 95%CI of Pb in different bullet types.

been known that Pb is the main metal com-posite of all bullets. However, many metalsare added to modify them properly for varioushandguns.(6,9) Annest et al found that LB mightcontain other metals with up to 26 elements.(10)

We also found many metals; Pb, Cu, Zn andNi; in all types of bullets, even in LB that was

80 Duronkadech P, et al.

not covered by any metal sheath. Though allfour metals were found in every type of bullet,only Pb and Cu, including their proportion, weresignificantly high and different among them.

The Pb level was significantly differentamong LB, SJ and FJ. However, the 95%CIof the Pb level showed that it could be used todistinguish only FJ from LB and SJ. If the Pblevel was between 24,985.51 and 28,004.02µg/L, it could not indicate whether the bulletswere LB or SJ. Pb has not been mentioned asa composition in FJ. Only Cu, Zn and Ni ortheir alloy were reported as found in theirjackets.(6,9,10,11) The Pb found on FJ in thisstudy might be due to contamination from bul-let coating substances, dirt inside the barrelsor particles dashed from the bottom of thebullets, which were uncovered by the jackets.

Cu was found in all bullet types. In spite ofits significantly lower amount in the LB groupthan in the other two bullet types, the 95%CIof Cu level disclosed that it had no potential toseparate any type of bullets from each other.

Considering each element separately, wefound that no single metal level was specificto each bullet type. However, when Pb andCu levels were put together as proportions, theresult showed that they had a significant dif-ference between each bullet type, and the 95%CI of this Pb/Cu ratio indicated that they werevaluable for identifying types of bullets. TheFJ had a ratio of less than 7.13, whereas theratio for SJ was between 94.61 and 584.73,and the LB had a ratio of more than 1,314.12.Using this Pb/Cu ratio can overcome theproblem of no single metal level being specificto each type of bullet.

The results of metal compositions in eachtype of bullet will lead to further study on trans-ferring metal elements from a projectile to thetarget. Subsequently, it would help to ascer-tain the type of bullet used for the victims byidentifying the Pb/Cu proportion from thewound.

Figure 3. 95%CI of Cu in different bullet types.

Composition of metals on fired bullets 81

ConclusionThe result of our study showed that lead,

copper, zinc and nickel could be found onevery bullet retained from inside the deadgunshot victims, whether they were leadbullets, semi-jacketed bullets or full metal jacketbullets. While zinc and nickel were found in afew cases, lead and copper were found inconsiderably more. Also, the lead and copperproportion was significantly different amongall three types of bullets.

AcknowledgementThe Authors would like to thank the Faculty of

Medicine, Chiang Mai University for providingfinancial support for this project, the ResearchInstitute for Health Sciences for offering theinstruments and Dr.Weerawan for supervising themetal analysis.

References1. Teret SP, Webster DW, Vernick JS, et al. Support

for new policies to regulate firearms: results of twonational surveys. N Engl J Med 1998; 339:813-8.

2. Smith TW, Smith RJ. Changes in firearm owner-ship among women, 1980-1994. J Crim Law Criminol1995;86:133-49.

3. Cook PJ, Ludwig J. Guns in America: results of acomprehensive national survey on firearms owner-ship and use. Washington, D.C.: Police Founda-tion, 1996.

4. National Center for Injury Prevention and Control,Centers for Disease Control and Prevention. Injurymortality statistics. Available at: http://wonder.cdc.gov/mortICD9J.shtml. Accessed January 10, 2002.

5. Knight B. Forensic pathology. 3nd ed. London:Arnold; 2004. p. 248.

6. Vincent JM. Di Maio. Gunshot wounds. 2nd ed.New York: CRC Press LLC; 1999. p. 25-8.

7. Wikipedia the free encyclopedia. Bullet. Availablefrom URL:http://en.wikipedia.org/wiki/Bullet Ac-cessed 18 Jan 2007.

8. Bullet types. Available from URL:http://matrix.dumpshock.com/raygun/basics/bullets.htmlAccessed 18 Jan 2007.

9. Handbook of Forensic Services. Elemental analysisexaminations. 1999;[2 screen]. Available at:URL:http://www.fbi.gov/hq/lab/handbook/examelem.htm. Access June 3, 2003.

10. Firearms Tutorial. Criminalistics Laboratory meth-ods.1998;[5 screen]. Available at:URL:http://www:meclib.med.utah.edu/WebPath/TUTORIAL/GUNS/GUBLAB.htm. Accessed October 22, 2004.

11. Brazeau J, Wong R. Analysis of gunshot residueson human tissues and clothing by X-ray microfluo-rescence. J Forensic Sci 1997;42:424-8.

82 Duronkadech P, et al.

องคประกอบของโลหะบนหวกระสนปนชนดตางๆ ทผานการยง

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