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Microscopic and macroscopic comparisons of 0.223 soft point and full metal jacket ammunition with bos taurus scapulae as a proxy to human flat bones
  1. Seth C Taylor1,
  2. D C Kieser2,3,
  3. N Hammer4,5,6,
  4. A Pullen1,7 and
  5. G Hooper1
  1. 1 Department of Orthopaedic Surgery and Musculoskeletal Medicine, University of Otago Christchurch, Christchurch, New Zealand
  2. 2 Orthopaedics, University of Otago, Dunedin, Otago, New Zealand
  3. 3 Medical Corps, New Zealand Defence Force, Dunedin, New Zealand
  4. 4 Fraunhofer Institute for Machine Tools and Forming Technology, Dresden, Germany
  5. 5 Department of Macroscopic and Clinical Anatomy, Medical University of Graz, Graz, Austria
  6. 6 Department of Trauma, Orthopedic and Plastic Surgery, University Hospital of Leipzig, Leipzig, Germany
  7. 7 Balllistics and Personnel Protection, New Zealand Defence Force, Devonport, Auckland, New Zealand
  1. Correspondence to Seth C Taylor, Department of Orthopaedic Surgery and Musculoskeletal Medicine, University of Otago Christchurch, Christchurch 8011, New Zealand; 22sethtaylor{at}gmail.com

Abstract

Background The prevalence of civilian 0.223 ammunition is widespread. Due to low costs and the same dimensions as a 5.56×45 mm North Atlantic Treaty Organization, this round is exceptionally popular. However, recent mass shootings have employed soft point (SP) expanding ammunition to cause grievous wounds compared with military full metal jacket (FMJ) rounds that do not rapidly expand on impact.

Methods The aim of this given study is to compare FMJ and SP rounds to determine if there are diagnostic differences between the bullet types in the wounds inflicted to flat bones. Bos taurus scapulae were used for 25 m simulated cranial gunshot injuries. Scanning electron microscopy was employed to assess the difference in wound morphology and elemental analysis between SP and FMJ rounds.

Results Entrance and exit wound morphology change significantly between the two different types of ammunition as seen with circumferential delamination which is indicative of FMJ rounds and is not seen with the softer SP hunting rounds. Lead staining of the entrance wound is visible on only the SP rounds.

Conclusion Gunshot flat bone wound morphology is distinctively different between SP and FMJ rounds. Circumferential delamination is only seen with FMJ due to the hardness of the round. Lead staining is only seen with SP rounds due to bullet composition.

  • anatomy
  • trauma management
  • adult pathology
  • forensic pathology
  • head & neck imaging

Data availability statement

Data are available on reasonable request. Data stored in a data repository and available on request from the corresponding author.

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Key messages

  • Recent mass shootings have employed soft point (SP) expanding ammunition to cause grievous wounds.

  • Scanning electron microscopy was employed to assess the difference in wound morphology and elemental analysis between SP and full metal jacket (FMJ) rounds.

  • Gunshot flat bone wound morphology is distinctively different between SP and FMJ rounds.

  • Lead staining of the entrance wound is visible on only the SP rounds.

  • Entrance and exit wound morphology change significantly between the two different types of ammunition.

Introduction

The prevalence of civilian 0.223 calibre ammunition is widespread internationally. Due to low costs and having the same dimensions as the 5.56×45 mm North Atlantic Treaty Organization, interchangeability of the rounds is easily permissible. Although the same dimensions, the 0.223 has lower pressures than the 5.56×45 mm cartridge. Due to higher pressures when fired, the 5.56×45 mm cartridge is not recommended to be shot through a rifle chambered solely in 0.223.1 However, 0.223, due to its lower pressures can be shot through a rifle chambered in 5.56×45 mm. The 0.223 round is commonly used for target shooting, vermin and small predator hunting due to its relative low costs and long-range abilities.1 However, as conflicts rage worldwide, soft point (SP) civilian ammunition has been used in the battlefields of Syria and Libya.2 3 Although solid lead ammunition fouls the breach and barrel far more quickly than its copper platted counterparts, it is a popular hunting round due to its rapid expansion on impact.1 4

Expanding ammunition has been banned on the battlefield since the Hauge Convention of 1899 due to the grievous wounds the ammunition produces.5 The Hague Convention stated that: ‘The contracting parties agree to abstain from the use of bullets which expand or flatten easily in the human body, such as bullets with a hard envelope which does not entirely cover the core or is pierced with incisions’. The Boer War (1899–1902) saw the use of ammunition developed by the British military in the Indian ammunition works in Dum Dum. These rounds were responsible for excessive morbidity due to the increased trauma caused by the bullet due in fact to the devastating rapid expansion of the soft lead bullet.6

Full metal jacket (FMJ) rounds comprise a zinc/copper coating over a mild steel or lead core and cycle through automatic and semi-automatic weapons much better due to the ease of loading from the magazine into the breach.1 FMJ bullets do not expand on impact creating a smaller and deeper temporary cavity compared with their SP equivalents, which can have upwards of 200% expansion on impact and are designed to dump all of their kinetic energy early causing massive damage compared with their FMJ counterparts (Table 1).7

Table 1

Bullet types, composition, and wound types associated with ammunition used for this study

Our intention was to expand on the works of Rickman and Smith which looked at SP and FMJ rounds under magnification as a diagnostic tool with bovine scapulae which found SEM analysis can used when entry/exit wounds cannot be determined from macroscopic assessment as well as producing more samples for the validity of using SEM analysis in the courtroom.8 Also, Fragkouli et al who looked at fracture patterns of SP and FMJ rounds with postcranial porcine flat bones who found significant differences between FMJ and SP rounds in the entry and exit wounds and that with the FMJ rounds directionality may be concluded due to entrance wound morphology.9 Additionally, our aim was to assist future medical investigations and gunshot-related forensic cases as researchers attempt to conclude the type of bullets used in deadly shooting events from intermediate range with SP and FMJ ammunition shot out of a common battlefield rifle travelling with similar velocities.

Materials and methods

Bos taurus scapulae

Bos taurus scapulae have two cortical layers surrounding a central cancellous bone section, which equivalents the human crania.8 Bos taurus scapulae are relatively easy to acquire in large numbers through the human food chain, making the requirement for ethical approval unnecessary. After slaughter, and a 7-day ageing process, the cow was butchered, and the scapulae were selected and taken to the range for ballistic investigation. The ageing process in a 3°C cooler and the delay in shooting the scapulae were judged acceptable as the only other alternative was to have the cow butchered directly for the scapulae. This was viewed as ethically and financially problematic. The bovine scapulae were all males aged between 16 and 36 months as per New Zealand butchery standards.10

Ammunition

For this experiment, 35 rounds were shot per calibre. The two rounds used in this study were a Fiocchi Munizioni (Lecco, Italy) 3.56 g, 0.223 FMJ (muzzle velocity 980 m/s, muzzle energy 1709 J) and a Prvi Partizan (Užice, Serbia) 3.56 g 0.223 SP (muzzle velocity 990 m/s, muzzle energy 1745 J).4 11

Experimental setting

An outdoor shooting range was used for this study. Bos taurus scapulae were used to simulate a proxy to human crania due to their similar morphological structure as human frontal bones . All scapulae were shot from a distance of 25 m from the prone position with the scapulae anchored with wire to an A-Frame target stand. This distance was chosen to simulate recent urban sniping conditions experienced in the Middle East (Syria and Libya).12 13

Chronograph

A Caldwell Ballistic Precision Chronograph (Caldwell Shooting Supplies, Colombia, Missouri, USA) was used to asses velocity.

Velocity assessment

Velocity was assessed using a Caldwell Ballistic Precision Chronograph at 25 m (factory calibrated to within±0.25% accuracy and measures from 5 to 9999 feet per second). Thirty-five rounds of SP and FMJ were shot through the chronograph and the mean and SD were calculated.

Metrics

A total of 35 FMJ and 35 SP rounds were fired. After the scapulae had been shot, they were left to dry in open air outside for 1 month.

Once the scapulae had dried, they were cleaned, photographed and preliminary measurements were taken on entrance/exit wounds, including fracture types, lengths of fractures, bevelling, presence of radiating fractures, circumferential delamination and the extent of bone loss. Cranial fracture types were assessed and recorded following standards set out by Brickley and McKinley.14

Table 2 illustrates fracture characteristics for entrance and exit wound, muzzle velocity, bevelling, the presence of radiating fractures and circumferential delamination and the thickness of the scapulae where the measurements were taken. All measurements for the 35 rounds per calibre were averaged.

Table 2

Fracture assessments.

Scanning electron microscopy

Specimens were prepared for SEM analysis by mounting the samples on an aluminium plate using double-sided carbon tape. They were coated with typically 2–20 nm of platinum using a Jeol JFC-1600 high-resolution sputter coater. The platinum coating enabled acceptable imaging without causing interference to elemental analysis. The projectiles underwent imaging and elemental analysis using a SEM electron dispersive X-ray spectrometer (SEM-EDS). The SEM was a Jeol 6610 with a Bruker XFlash 5030 EDS system (JEOL, Tokyo, Japan).

Imagery of the entrance and exit wounds were captured using a secondary detector performed at an accelerating voltage at either 10 or 25 kV, a beam current of 40 μA and a spot size of 50.

To highlight the atomic number contrast and identify different areas within the sample for elemental analysis, a backscatter detector was used. Imaging was performed at an accelerating voltage of 25 kV. EDS analysis was performed at an accelerating voltage of 25 kV, using a beam current of 40 μA and a spot size of 50. The EDS spectra were captured until 250 000 counts had been amassed, as appropriate for quantifying minor alloying elements.

Results

Velocity assessment

Velocity was assessed at 25 m from point of impact using the Caldwell Ballistic Precision Chronograph, which returned an average velocity of 922 m/s (1530 J) (SD=12 m/s) for the SP round and 904 m/s (1417 J) (SD=11 m/s) for the FMJ round.

Entrance and exit wound morphology

Cranial fracture types were assessed and recorded following standards set out by Brickley and McKinley.14 All measurements were averaged (n=35).

Entrance and exit wound morphology

The entrance wound morphology of the SP rounds have a dark grey ring bordering the entrance wound, which does not appear on scapula used with the FMJ rounds. Under SEM magnification (8–9 times magnification), there is a clean circular entrance wound of the FMJ round (Figure 1), whereas the SP round entrance wound appears more uneven in appearance (Figure 2). The exit wound of the SP round (Figure 3) is larger and more ragged than the FMJ round (Figure 4).

Figure 1

0.223 full metal jacket entrance wound with circumferential delamination and radiating fractures.

Figure 2

0.223 soft point entrance wound with cancellous and cortical bone peeled back.

Figure 3

0.223 full metal jacket exit wound with 18 mm of bevelling.

Figure 4

0.223 soft point exit wound with 20 mm of bevelling.

Lead staining

Of the 35 rounds of 0.223 SP shot into Bos taurus scapulae, all 35 entrance wounds presented visible lead staining to some extent from the SP 0.223 hunting rounds after 1 month of sitting outside in open air (Figure 5). This was confirmed using SEM-EDS analysis which showed that lead was present on all samples analysed. In contrast, although the SEM detected lead on the FMJ samples, lead staining was not visible despite the samples being kept in the same conditions.

Figure 5

0.223 soft point lead staining is visible around the circumference of the entrance wound.

Discussion

The presence of lead staining of bone has been documented in archaeological and forensic cases. Lead bullets all have the ability to stain bone with a greyish hue.15 16 The presence of lead staining was noted in this study. When exposed to air, lead tarnishes to a dull grey colour.17 However, none of the 0.223 FMJ exhibited lead staining. It should be noted that FMJ rounds shot in this study contained a copper and zinc alloy jacket surrounding a lead core, whereas the 0.223 SP is a soft lead bullet encased by a stronger metal jacket, left open at the tip.1 Radiating fractures were only present with the FMJ rounds and were short with an average of 5.5 mm (SD=1.6). Radiating fractures are only present with the FMJ rounds which is interesting as the SP round is faster (SP 922 m/s vs 904 m/s FMJ). The softness of the lead-tipped bullet could be the reason there are no radiating fractures as the FMJ round is harder and crushes bone, whereas SP is softer and mushrooms on impact. If the kinetic energy of the bullet is high enough, radiating fractures may form. Radiating fractures starting from the point of ballistic impact will follow the path of least resistance.18 The short length of the radiating fractures could be caused by the robustness of the flat bone due to the lack of cranial sutures.19 Moreover, the lack of a liquid-filled bladder like a human cranium (brain material is classified a liquid) causes an immense amount of pressure inside the head (can cause the rupture of the cranium causing much more damage and allowing radiating fractures to become much more longer and pronounced as velocities increase.1 20

The SP entrance wounds are more ragged in appearance suggesting immediate deformation of the projectile on impact.7 18 19 The SP rounds also lack circumferential delamination found on the FMJ rounds. Circumferential delamination is only present on the entrance wounds of the FMJ rounds. This comes as no surprise as it is well documented and indicative of FMJ as it crushes the bone due to the hard non-expanding nature of the round.1 21 Entrance wound size correlates well with previous studies, where 5.56×45 mm FMJ, which is the military version of 0.223, returned entrance wound sizes of similar proportions (6.5 mm) for the FMJ rounds.15 22 The 0.223 SP rounds also had similar entrance wound diameters to the 0.22 LR (8 mm).7 15 Entrance wound size was indicative of round type. The harder FMJ round was smaller (6.5 mm SD=0.4), while the SP round was larger due to the expanding nature of the round (8 mm SD=0.8) Exit wound bevelling was also larger with the SP round due to the expansion of the soft lead bullet. This should come as no surprise as the bullet impacts the target, it is designed to expand up to 200% of its original size.19

The presence of lead staining of bone has been documented in archaeological and forensic cases. Lead bullets all have the ability to stain bone with a greyish hue.16 17 The presence of lead staining was noted in this study. When exposed to air, lead tarnishes to a dull grey colour.23 However, none of the 0.223 FMJ exhibited lead staining. It should be noted that FMJ rounds shot in this study contained a copper and zinc alloy jacket surrounding a lead core, whereas the 0.223 SP is a soft lead bullet encased by a stronger metal jacket, left open at the tip.1 12

Under SEM magnification, the entrance wound of the FMJ round is uniform in appearance and clean, with the margins crushed that are clearly visible under magnification. Moreover, the SP round is completely lacking a uniform entrance wound, due to the fact that rapidly expanded bullet caused the trabecular bone (lattice work in appearance) to be pulled upwards as the bullet passed through the bone. The exit wound of the SP round is larger, and far more destruction has occurred and visible under magnification. The FMJ round is smaller and has a cleaner appearance which should come as no surprise due to the nature of the bullet, as it was designed to cause less damage than the SP counterpart. These findings match well with SEM study by Rickman and Smith, where they were able to distinguish FMJ versus the SP rounds microscopically as well as with the study by Fragkouli et al, who macroscopically could distinguish entrance and exit wound morphology between SP and FMJ rounds.

However, there are limitations to this study. Fresh scapulae were not available as it was problematic to acquire scapulae from freshly slaughtered cattle. We were only able obtain 7-day aged beef stored at 3°C before from a local butcher before the experiments could be conducted. More research needs to be undertaken to substantiate these findings as the sample size was small (n=35) per bullet type and round selection due to financial constraints. Moreover, there was limited SEM availability and funding to analyse a greater sample size.

Conclusion

SP scapulae gunshot injuries display more ragged entrance wounds with larger bone defects and radiating fractures. Circumferential delamination is also distinguishable between FMJ and SP rounds as zero of the 35 SP rounds exhibit the crushed entrance wound indicative of FMJ rounds. Lead staining is also a diagnostic tool which can differentiate from FMJ rounds during a pathological investigation.

This study has found lead staining is visible macroscopically on all 35 gunshot wounds shot with SP rounds and is not present on any of the FMJ rounds. Also, lead was detected on the SP rounds and confirmed using SEM-EDS analysis. Circumferential delamination is also visible under SEM magnification that can be used as a diagnostic tool. The SP round that has rapidly expanded causing trabecular bone (lattice work in appearance) to be pulled upwards (peeled back appearance) as the bullet passed through the bone is clearly distinguishable between the FMJ round and can help from a legal medicine standpoint to discern between an FMJ and an SP round.

Data availability statement

Data are available on reasonable request. Data stored in a data repository and available on request from the corresponding author.

Ethics statements

Patient consent for publication

Ethics approval

Bos taurus scapulae were acquired from a local butcher. Due to the origin of the tissues from the food chain, no study or ethical approval was deemed necessary.

Acknowledgments

The experimental study described in this paper was conducted during the course of a Forensic Anthropology PhD undertaken by the author, Seth C. Taylor, at the University of Otago in 2018/2019.

References

Footnotes

  • Twitter @pulla106

  • Contributors SCT: main author as research was undertaken in course with a PhD programme. DCK, NH and GH: supervisors and editing. AP: statistical analysis.

  • Funding Funding for this study project was provided by the University of Otago.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.