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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 8  |  Issue : 3  |  Page : 97-103

Distinctive bullet impact holes by 9-mm caliber projectile on sheet metal surfaces


1 Forensic Science Programme, School of Health Sciences, Health Campus, Universiti Sains Malaysia, Kubang Kerian, Kelantan, Malaysia
2 Department of Chemistry, Division of Criminalistics, Forensic Science Analysis Centre, Petaling Jaya, Malaysia

Date of Submission28-Nov-2021
Date of Decision21-Feb-2022
Date of Acceptance22-Feb-2022
Date of Web Publication02-Sep-2022

Correspondence Address:
Kah Haw Chang
Forensic Science Programme, School of Health Sciences, Universiti Sains Malaysia, Kubang Kerian 16150, Kelantan
Malaysia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jfsm.jfsm_83_21

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  Abstract 


Introduction: A comprehensive scene reconstruction requires forensic investigators to examine the impact marks left on various surfaces to identify whether a projectile produces a specific hole. Subsequently, it is further necessary to determine whether a particular ammunition has caused the impact. Throughout history, designs of ammunition have evolved with the intended effects, which could leave different impact marks on a target surface, especially by ammunition with a nonconventional design. Careful examination on impact marks and determination of their specific characteristics on sheet metal of vehicle would provide crucial forensic information. Aim: This study was aimed to physically characterize bullet impact holes made by 11 types of 9-mm caliber ammunitions. Materials and Methods: Two automotive doors were shot with different ammunitions from the same firearm, and the morphological features of bullet impact holes were observed and compared. Results: Bullet impact holes produced by the various ammunitions could be differentiated through careful observation of bullet hole circumferences, presence of petalling effect, metallic ring and triangular peak at the edge, and deposition of residue at the peripheral area of bullet impact holes. Ammunitions with nonconventional design such as Inceptor-Polycase and GECO Hexagon showed observable morphological differences and discriminated them from bullet impact holes made by conventional ammunitions. Conclusion: A thorough physical examination could aid in distinguishing bullet impact holes and predicting the possible types of ammunition that had made an impact hole on a surface.

Keywords: Forensic science bullet hole, physical examination, Introduction, projectile, sheet metal


How to cite this article:
Abd Malik SA, Nordin FA, Mohd Ali SF, Lim Abdullah AF, Chang KH. Distinctive bullet impact holes by 9-mm caliber projectile on sheet metal surfaces. J Forensic Sci Med 2022;8:97-103

How to cite this URL:
Abd Malik SA, Nordin FA, Mohd Ali SF, Lim Abdullah AF, Chang KH. Distinctive bullet impact holes by 9-mm caliber projectile on sheet metal surfaces. J Forensic Sci Med [serial online] 2022 [cited 2022 Dec 7];8:97-103. Available from: https://www.jfsmonline.com/text.asp?2022/8/3/97/355571




  Introduction Top


During a firearm-related crime scene investigation, forensic investigators must identify any direct and indirect forensic traces and maximize the available information for meaningful interpretation.[1] Information retrieved from forensic examination of cartridge case and spent projectile can aid in determining the types of ammunition and firearm involved in shooting. However, spent cartridge case might only be recovered from shooting scene involving firearm equipped with ejection mechanism. On the other hand, fired bullets might have undergone deformation or completely unfound at the shooting scene. Therefore, bullet impact holes found in a crime scene could provide useful information related to a shooting activity, needing greater investigative efforts.[2],[3]

Bullet impact holes left on sheet metal surfaces, especially in a vehicle-related shooting scene, warrant special attention by the investigative team. Careful examination might lead to a more accurate determination of the direction, distance and sequence of shooting, as well as the possible types of firearms used in the shooting.[4],[5] Additionally, it is also important to establish whether a particular impact mark or hole is made by a projectile of a particular type of ammunition. In cases where multiple marks and holes are encountered, it is crucial to determine if they are made by a single kind of projectile or otherwise.[4],[5] Careful examination on a bullet hole present on surfaces, especially metal sheet, could possibly allow us to establish bullet caliber,[6] bullet nose,[7],[8] impact velocity,[6],[8],[9] and the impact angle.[5],[10],[11] The examination of bullet holes on sheet metals can aid in estimating firing distance[6] and predicting the flight trajectory.[12] To a certain extent, the projectile that made an impact can also be predicted,[7],[8] at least for the investigator to narrow down to a smaller number of possible ammunitions and firearms that could have involved.

Although many of the works mentioned earlier could have provided significant contributions to confirm the occurrence of shooting event and aid in reconstructing the crime, detailed examination on bullet impact holes should be conducted for defensible forensic conclusion. Current development and advancement in firearm and ammunition industries had contributed to the expansion on a variety of ammunitions in the market, fulfilling the requirements of manufacturers and users. Moreover, drive-by shooting case is on the rise, especially with unknown source of firearm and ammunition. Therefore, the physical examination of bullet impact holes certainly deserves further exploration. In this study, 11 types of 9-mm ammunitions of different designs were fired from the same firearm toward two sheet metals of different vehicle manufacturers. Through physical examination, deformation pattern and damage characteristics of each bullet impact hole were investigated. It is hoped that the specific characteristics determined (if any) could pave the way for law enforcement authorities to link the possible types of ammunition that had made an impact on a surface.


  Materials and Methods Top


Shooting and sampling

A semi-automatic pistol Sig Sauer model SP 2022 (Schweizerische Industrie Gesellschaft and J. P. Sauer and Sohn, Switzerland) was used for shooting. Eleven types of 9-mm caliber ammunition were supplied by the Royal Malaysia Police as follows:

  1. SME (Full Metal Jacket [FMJ], Round Nose, 115 g/7.45 g, Selangor, Malaysia)
  2. Sellier and Bellot (FMJ, round nose, 115 g/7.45 g, Prague, Czech Republic)
  3. Arms Corporation (FMJ, round nose, 124 g/8 g, Marikina City, Philippines)
  4. Sellier and Bellot (Jacketed Hollow Point (JHP), 115 g/7.45 g, Prague, Czech Republic)
  5. Remington Arms Company (JHP, 115 g/7.45 g, Connecticut, United States)
  6. Royal ammunition Co. (JHP, 115 g/7.45 g, Nakhon Sawan, Thailand)
  7. Arms Corporation (JHP, 115 g/7.45 g, Marikina City, Philippines)
  8. Bullet Master Co. (Lead Round Nose [LRN)], 135 g/8.7 g, Kanchanaburi, Thailand)
  9. Ruag Ammotech (Jacketed Deform Projectile (JDP), Round Nose, 99 g/6.4 g, Bern, Switzerland)
  10. Inceptor-Polycase (Advance Rotation Extreme (ARX), 65 g/4.21 g, Georgia, United States)
  11. GECO (Hexagon [HEX], 124 g/8 g, Troisdorf, Germany).


Shooting experiments were performed at the shooting range of Police Training Centre Kuala Lumpur (PULAPOL), Malaysia. Prior to shooting, the sheet metal, i.e., door panel (held intact by the car door frame with interior accessories and window removed), was placed on top of a bench in a vertical position and held tightly by iron rods. The outer door panel was positioned in front of the shooter. At a three-meter distance from the target, three shots using the same type of ammunition were fired to the target by a trained shooter at 90° level, leading to formation of bullet holes. Subsequently, shots from other ammunitions were also fired using the same firearm onto the same sheet metal. In this study, two types of metal sheets were used, namely from vehicles of BMW E46 (Munich, Germany) and Honda Civic ES (Tokyo, Japan).

Visual examination and comparison

Visual examination of bullet holes was made using magnifying glass in situ followed by stereomicroscope. A Leica Microscope MZ 16 (Switzerland) equipped with a digital camera (Leica FC 290) was used. Light source was supplied by transmitted light base (Rottermann, TL RC 1). The system was supported by Leica Application Suite software (Switzerland) for photo capturing. The area of metal sheets with bullet holes was placed on the stage of the microscope using plasticine to fix it from moving for microscopic examination. Each bullet hole was magnified, photographed, and saved as TIFF files. Impact marks produced by the projectiles tested in this study were evaluated, and any characteristic directed to the specific type of ammunition was investigated.


  Results Top


Visual examination and comparison on bullet holes

All projectiles successfully perforated the target leaving bullet holes. As expected, both metal sheets from the two different car brands were not able to stop projectiles of relatively high kinetic energy from perforation. In our case, this study was designed to simulate drive-by shooting event at a fixed shooting distance, and therefore, the velocity of projectile before and after perforation was not measured. As malleable material, sheet metals do not crack upon impact but deformed and bent toward the direction of projectile traveling path.[5],[11] In fact, bullet holes produced on the two sheet metal surfaces were very similar through visual observation when the same type of projectiles struck on them, indicating that the formation of bullet impact hole was less likely to be influenced by different sheet metals used in this study. Note that the thickness of these two sheet metals was measured at 0.96 mm and 1.02 mm, respectively, and they are made up of galvanized steel. The metal sheets from the car door of BMW E46 were found slightly thinner as compared to car door of Honda Civic ES. The exact composition of these sheet metals was not determined in the study. Nonetheless, if trace residue around circumference of a bullet hole was concerned to confirm the cause, a thorough analysis on the elemental composition of metal sheet substrate is recommended for comparison and determination.

Shape of bullet impact holes

In this study, majority of the ammunitions were of conventional designs with rounded nose section. In addition to these common projectiles, nonconventionally designed ammunitions were also considered, including ARX and HEX [Figure 1].
Figure 1: Nonconventional designed ammunitions: (a) Advance Rotation Extreme and (b) Hexagon

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All the entry holes on the metal sheets were observed in this study. Upon impact, circular holes were observed with orthogonal angle impact by majority of the projectiles used in this study on the two sheet metals [Figure 2]a.[10],[11],[12] In fact, the circular holes formed on the sheet metal were not found exactly perfect although with orthogonal angle impact as the substrates were not completely flat due to the nature of a car door design. Therefore, certain bullet impact holes might be appeared slightly ovoid depending on the site of impact [Figure 2]b. The averaged dimension of respective bullet impact holes is demonstrated in [Table 1]. In this study, two exceptional observations were noticed on bullet holes made by ARX [Figure 2]c and HEX [Figure 2d] projectiles. These respective bullet holes appeared distinctive from the smooth round or ovoid shape as demonstrated in most projectiles. Abnormal-shaped ARX and HEX projectiles could have caused the segment with no smooth circumferences of bullet holes.
Figure 2: Orthogonal view of bullet holes at entry point with (a) circular shape, (b) ovoid shape, and irregular shapes made by (c) Advance Rotation Extreme and (d) Hexagon projectiles

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Table 1: Dimensions of bullet impact holes made by different ammunition types

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Crater formation

Formation of crater on the exit face was evident in every instance of shooting events, regardless of projectiles that perforated the targets. Our detailed examination showed that the degree of deformation reduced gradually from the exact point where a projectile struck toward the peripheral areas of bullet hole. Haag and Haag[5] and Atkins et al.[7] suggested that such phenomenon could be due to elastic nature of metal sheet to account for minimum relaxation of material after the passage of projectile, in addition to acceleration of metal material away from the margin of a hole by the projectile. [Table 1] shows the averaged diameters and depths measured from bullet holes caused by the 11 types of ammunitions tested in this study. In general, the diameters of bullet holes produced by projectiles from the ammunitions of FMJ, LRN, and JDP types were <9 mm. By comparison, projectiles of ARX type had produced bullet holes with larger size, mainly due to the formation of abnormal-shaped bullet holes upon perforation, as demonstrated in [Figure 2]c.

Kruskal–Wallis test was performed using IBM SPSS Statistics version 26.0 (SPSS Inc., Chicago, IL, USA) to investigate if there are significant differences between the six groups of ammunitions on the diameters and depth of the bullet holes produced upon perforation. P < 0.05 was considered statistically significant in this test. [Table 2] demonstrates the statistical output from Kruskal–Wallis test among six groups of ammunitions. Considering the medians of the bullet holes' diameters by the six ammunitions, the P values are less than the significance level of 0.05, indicating that the median diameters of bullet hole differ for at least one type of ammunition (P < 0.001). Post hoc analysis for multiple comparisons was carried out using Mann–Whitney tests to identify which pairs of groups differ significantly from one another. The significance value was adjusted to 0.003 (0.05/15) based on 15 possible combinations among the groups. The median diameters of bullet holes produced by the projectiles of FMJ ammunitions were likely to be smaller than JHP (P < 0.001).
Table 2: Results from Kruskal-Wallis test among six types of ammunitions on the measurement of diameter

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Based on the types of projectiles causing the holes, the depth of craters varied from 3.65 to 7.53 mm. Bullet holes caused by JHP projectiles were found to be shallower, measured between 3.65 and 3.85 mm. On the other hand, the depth measured from the bullet holes formed by the three FMJ projectiles was greater (i.e., 5.01–5.15 mm). [Table 3] shows the statistical results from the Kruskal–Wallis test carried out on the measurement of the depth of bullet holes. The Kruskal–Wallis test indicated a statistically significant difference in the depth of bullet holes among the six ammunition types (P < 0.001). Post hoc test suggested the difference in the median depth of the bullet holes, where the bullet holes produced by FMJ ammunition were likely to have deeper crater than JHP (P < 0.001).
Table 3: Results from Kruskal-Wallis test among six types of ammunitions on the measurement of diameter

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Special designed ammunitions were found to have produced crater of greater depth as seen in ARX and HEX although they were fired from the same distance. Additionally, the craters observed in bullet hole made by LRN projectiles were also relatively greater in-depth as compared to other conventional ammunitions. The formation of petals at the impact bullet holes had caused greater depth craters on the metal substrate.[6] The velocity of the projectile hitting the metal sheet and the rate of projectile deceleration as it passed through the metal sheet could have contributed to variation in the depth of craters. It was also worth noting that the greater depth craters could have also contributed to larger variations up to 14.6%, suggesting that the petals produced at the bullet holes were slightly different in their respective dimension. From our observation, the diameter and depth of crater could contribute to discrimination of bullet impact holes made by projectiles of FMJ and JHP types, even they showed very similar shape and pattern.

Petalling effect

Petalling effect is the formation of flower-like appearance at the edge of the crater.[6] Such effects were found on the bullet holes produced by ARX and HEX projectiles [Figure 3]a, [Figure 3]b. According to Gupta et al.,[8] conical shape projectile caused small hole at initial stage of impact. It was followed by propagation of crack way beyond the circumference of the projectile, leading to the formation of petals. It was worth noting that the petalling had also contributed to segmented circumferences of bullet holes. A half radial “petalling effect” was observed on those bullet holes made by LRN projectiles [Figure 3]c. Such observation was also known as small splits, and they were usually absent in the bullet impact holes produced by jacketed bullets [Figure 3]d.[10] A LRN bullet is not conical in nature, but due to its soft leaded material, petal might be formed with the destruction of projectile during impact where its shape becomes conical like. On the contrary, other projectiles having round-ended shape tip formed smooth radial crater at bullet hole lip.[10],[12]
Figure 3: Petalling effect at exit point of bullet impact hole made by (a) Advance Rotation Extreme, (b) Hexagon, (c) Lead Round Nose, and (d) Full Metal Jacket projectiles

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Metallic ring at the internal circumference

Metallic ring, arisen from the deposition of material originated from projectile onto the internal circumference of bullet hole, was observed among the bullet impact holes. Transfer of residues occurred upon the impact of high-speed and high-temperature projectile onto the high resistant metal sheet. Although metal was a medium possessing less capability in allowing such transference,[5] the successful deposition of metallic ring residues onto the surface was possible but restricted by the types of projectiles.

Prominent metallic ring was observed at the bullet impact holes produced by JDP-type projectiles [Figure 4]a as compared to other projectiles. Golden-brown-colored residues were believed to have transferred from the projectile. Bullet holes caused by FMJ projectile [Figure 4]b were found to have contained lighter metallic ring in slightly black color around internal circumference. This could be due to the stripping of bullet jacket onto the metal substrate upon strong shearing interaction.[6] On the contrary, no metallic ring could be observed on those holes made by JHP, ARX, HEX, and LRN projectiles [Figure 4]e, [Figure 4]f, [Figure 4]g, [Figure 4]h.
Figure 4: Metallic ring seen on bullet holes impacted by (a) Jacketed Hollow Point, (b) Full Metal Jacket, (c) Jacketed Hollow Point, (d) Advance Rotation Extreme, (e) Hexagon, and (f) Lead Round Nose projectiles

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Heavy deposition of visible residues at the peripheral area of bullet impact holes

In this study, another significant physical observation was evident on the entry side of bullet holes made by both LRN- and ARX-type projectiles. Visible residues were found deposited at the peripheral area of respective bullet holes, as demonstrated in [Figure 5]. Being relatively softer than those jacketed ones, these projectiles tend to disintegrate upon striking on relatively hard surface. Such heavy deposition was only found on the entry side of these holes and absent in all bullet holes perforated by other projectiles. Actual deformation phenomenon would be interesting to be observed by utilizing high-speed camera, perhaps in the future study, which could aid in understanding the terminal ballistic behaviors of these projectiles.
Figure 5: Heavy deposition of residues on bullet holes impacted by (a and b) Lead Round Nose and (c and d) Advance Rotation Extreme projectiles

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Triangular peaks at the internal circumferences

Unique pattern on the existence of triangular peaks was seen at the internal circumference of bullet holes made by the four JHP projectiles used in this study, regardless of their respective brands [Figure 6]. These projectiles tend to become “mushroom” and increase in their respective diameter upon impact. Subsequently, mushroomed projectiles could carry slightly segmented nose while they continued with their flight path, exiting the target surface. These deformed projectiles might no longer possess circular circumference. Formation of triangular peaks could happen after a very short instant of impact and caused by the deformed projectile, distinguishing them from the petals formed at the instance when the nonrounded projectile impacted on a surface. The observation was absent in bullet holes made by other projectiles.
Figure 6: Triangular peak pattern at the edge of crater viewed from exit face of (a-d) Jacketed Hollow Point bullet holes

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  Discussion Top


In general, bullet impact holes could be differentiated based on the respective characteristics produced on the metal substrate in relation to their morphological appearance. Deformation processes associated with malleable sheet metal surfaces were found contributing to different attributes. [Table 4] summarizes the observation on bullet impact holes made by different ammunition types.
Table 4: Summary of observation on bullet holes made by different ammunitions

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Formation of crater at the exit side of a target sheet metal was a definite observation upon striking of projectile, given that a projectile successfully perforated a surface. The most significant observation for differentiation was from those holes made by the respective ARX and HEX projectiles through petalling effect at the exit hole as well as the segmented bullet hole circumferences. Bullet holes struck by JHP projectiles exhibited prominent triangular peak pattern at the inner circumference, regardless of the ammunition manufacturers. Colored metallic rings could be seen on bullet holes due to perforation of jacketed projectiles, while it was commonly absent with unjacketed projectile impact. Heavy deposition of residue from projectile seen at the peripheral area of bullet holes could also be the characteristics for ARX and LRN projectiles.

Different designs of nose shape or the nose geometry had produced specific morphological features on the bullet impact holes. Furthermore, the jacketing on the core of the projectile had also significantly generated distinctive bullet impact holes although they had shared the same nose geometry. In this study, the two special ammunitions with nonconventional design, namely the Inceptor-Polycase ARX and GECO HEX, demonstrated severe petalling effect which had been absent in those conventional jacketed bullets. Further discrimination on the bullet impact holes caused by these two ammunitions could be observed through deposition of residues originated from the ARX projectiles.

Throughout the years, various ammunitions of different designs were produced to fulfill the intended uses. In view of this, a study on the bullet impact holes deserves exploration to keep pace with the current developments in firearm and ammunition aspects. Such comparative information is beneficial in providing clues for forensic investigation, especially when encountering any impact hole of unknown cause. Since this study only examined the physical characteristics of bullet impact holes made by projectiles of 9-mm caliber, different settings of shooting experiments shall be explored in future by varying the numbers and thicknesses of metal sheets, the distances between shooter and target, the shooting angles, as well as the distances between two metal sheets. It is also worth characterizing the bullet striations upon perforation to establish the target which had been passed through before stoppage of the projectile. As firearm-related cases have become more complicated with technological advancement, it would be crucial to gather extensive sources of ammunition for further data comparison. Nonetheless, further analytical work, simulating the real shooting case scenarios, is necessary for defensible characterization.


  Conclusion Top


Determination of impact hole characteristics made by a specific bullet through physical examination is crucial to aid in forensic investigation of shooting-related cases, especially when no cartridge case and/or projectile was recovered. In this study, distinctive bullet impact holes on the sheet metal produced by 11 ammunitions of 9-mm caliber were observed. These bullet impact holes could be possibly differentiated through careful examination of bullet hole circumferences, presence of petalling effect, metallic ring and triangular peak at the edge, and deposition of residue at the peripheral area of bullet impact holes. Ammunitions with nonconventional design such as Inceptor-Polycase and GECO HEX demonstrated observable morphological differences, allowing their discrimination from bullet impact holes made by conventional ammunitions.

Acknowledgments

The authors thank the financial support via the USM Short-Term Grant (304/PPSK/6315250).

Financial support and sponsorship

This study was financially supported by the Universiti Sains Malaysia Short-Term Grant (304/PPSK/6315250).

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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