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The Evolution and Examination of Firearms and Ballistics - Part 2

The Evolution of Ballistics

Firearms and ballistics have a rich history and an important role in both military / civilian and forensic sciences. This essay explores the evolution of firearms, types of ammunition, ballistic principles, and forensic examination techniques based on the "Handbook of Firearms and Ballistics: Examining and Interpreting Forensic Evidence" by Brian J. Heard.


This is the second of two parts; the information regarding ballistics, examination and forensic techniques.


This is not a complete write-up regarding the book, but more a summarization of the contents to help folks understand terminology.


*Please note that this book was originally printed in the late 90s based upon techniques from the 70's and 80's, and most of the photos are grainy at best:

There will be updated photographs to help visually contextualize the contents below.

 

Ballistics and Firearms Examination

Ballistics, the science of the mechanics of projectiles, is an integral field of study within both forensic science and firearms engineering. It is divided into three main categories: internal, external, and terminal ballistics. Each of these categories examines different phases of a bullet's journey, from the moment of firing to its final impact. Understanding these phases is crucial for enhancing firearm design and solving criminal cases.


Internal Ballistics

Internal ballistics deals with the events that occur within the firearm from the moment the trigger is pulled until the bullet exits the barrel. This phase encompasses several critical processes:

  • Ignition of the Propellant: When the trigger is pulled, the firing pin strikes the primer, igniting the propellant (gunpowder). This ignition creates a rapid expansion of gases.

  • Pressure Dynamics: The expanding gases generate high pressure within the cartridge, propelling the bullet forward. This pressure must be carefully managed to ensure consistent velocity and accuracy.

  • Bullet Travel through the Barrel: As the bullet travels down the barrel, it accelerates to its maximum velocity. The design of the barrel, including its length, diameter, and rifling (spiral grooves), plays a crucial role in stabilizing the bullet and improving its accuracy.

  • Rifling: The spiral grooves inside the barrel impart a stabilizing spin to the bullet, which helps maintain its trajectory and enhances accuracy. The specific pattern of rifling marks left on the bullet is unique to each firearm, making it essential for forensic identification.


External Ballistics

External ballistics examines the behavior of the bullet as it travels from the muzzle of the firearm to the target. This phase considers several factors that influence the bullet's flight:

  • Trajectory: The bullet follows a parabolic path influenced by gravity and initial velocity. The trajectory is a critical factor in determining the bullet's impact point.

  • Drag: Air resistance slows the bullet down, affecting its range and impact energy. The shape, mass, and velocity of the bullet influence the amount of drag it experiences.

  • Environmental Factors: Wind, humidity, and temperature can alter the bullet's path. These variables must be considered when evaluating a shot, particularly over long distances.

Understanding external ballistics is crucial for both shooters aiming to improve accuracy and forensic analysts reconstructing shooting incidents.


Terminal Ballistics

Terminal ballistics studies the behavior of the bullet upon impact with the target. This phase is essential for understanding the effects of the bullet on different materials and living tissues. Key aspects of terminal ballistics include:


  • Penetration: This measures how deeply the bullet enters the target, influenced by the bullet's velocity, mass, and shape, as well as the target's density and composition.

  • Expansion: Many modern bullets are designed to expand upon impact, increasing their diameter to cause more significant damage. This expansion is typical in hollow-point bullets used in self-defense and law enforcement.

  • Fragmentation: Some bullets are designed to break apart upon impact, creating multiple wound channels and causing extensive tissue damage. This is common in certain types of military and hunting ammunition.

  • Energy Transfer: The bullet transfers kinetic energy to the target, which determines its stopping power. High energy transfer can incapacitate the target more effectively.


Forensic Firearms Examination

Forensic firearms examination involves the meticulous process of identifying and comparing bullets and cartridge cases to specific firearms. This field is vital for criminal investigations, helping to link suspects to crime scenes. The examination includes several techniques:

  • Rifling Marks Analysis: Each firearm leaves unique rifling marks on a bullet due to the specific pattern of the barrel's grooves. These marks are unique to each firearm and can be matched to a suspect weapon.

  • Striation Patterns: Fine lines or grooves on the surface of a bullet, known as striations, are formed during the bullet's travel through the barrel. These patterns are unique and can be used to match a bullet to the gun that fired it.


  • Firing Pin Impressions: When the firing pin strikes the primer, it leaves a unique impression on the cartridge case. These impressions can be compared to identify the specific firearm used in a shooting. (See center of above image.)

  • Breech Face Marks: The rear face of the firearm's breech can leave distinctive marks on the cartridge case. These marks are useful for identifying the firearm used. (A better example of the surface area denoted by the purple arrow above. Think of it as microscopic topography of the flat side of the cartridge.)


Techniques in Forensic Examination

Forensic experts employ several sophisticated techniques to ensure accurate identification of firearms and ammunition:

  • Comparison Microscopy: This technique involves using a comparison microscope to simultaneously view two objects, such as a suspect bullet and a test-fired bullet, side by side. It allows forensic experts to compare microscopic details and determine if they match.

  • Mathematical Proof of Striation Matches: Advanced mathematical methods analyze striation patterns quantitatively. These methods help confirm whether two sets of striations are statistically likely to have come from the same firearm.

    • The modern method is called Congruent Matching Cells, or CMC, which divides the scanned surface of either the test round or culprits round into a grid of cells, then searches the other surface for matching cells. The greater the number of matching cells, the more similar the two surfaces, and the more likely they are to have come from the same gun.

  • Ballistic Gel Testing: Ballistic gel simulates human tissue and is used to test bullet performance under controlled conditions. This helps in understanding penetration, expansion, and energy transfer characteristics.


 

Case Studies and Applications

Forensic ballistics plays a critical role in solving crimes. By examining bullets and cartridge cases found at crime scenes, forensic experts can link evidence to specific firearms, reconstruct shooting incidents, and provide crucial information for legal proceedings. Case studies often illustrate the importance of meticulous ballistic analysis in achieving justice.


Modern Challenges and Innovations

The field of forensic ballistics continues to evolve with advancements in technology. Digital imaging, automated comparison systems, and 3D modeling enhance the accuracy and speed of ballistic examinations. However, challenges remain, such as the increasing use of improvised firearms and the need for standardized methods across forensic laboratories. Continued innovation and adaptation are essential to address these challenges and ensure the effectiveness of forensic ballistics in the future.


Forensic Techniques and Case Studies

Forensic firearms examination is a meticulous field that combines a variety of techniques to analyze evidence and solve crimes. This section delves into the specific methods used by forensic experts to estimate the range of firing, analyze bullet holes, examine gunshot residue, and restore erased serial numbers, as well as highlights notable case studies that demonstrate the application of these techniques.


Estimating the Range of Firing and Analyzing Bullet Holes

Determining the distance between the firearm and the target at the time of firing is crucial in forensic investigations. Several techniques are used to estimate this range:

  • Chemical Tests: Chemical tests, such as the Modified Griess Test, are used to detect the presence of nitrites around the bullet hole, which are byproducts of the gunpowder combustion. The distribution and concentration of nitrites can help estimate the firing distance. For instance, a higher concentration of nitrites typically indicates a closer range.

  • X-ray Photography: X-ray imaging is employed to visualize the internal structure of bullet holes, especially in cases involving complex wound channels or bullets lodged in bones. X-rays can reveal the trajectory and deformation of bullets or damage to the bodies internals, aiding in the reconstruction of the shooting incident.

  • Visual and Microscopic Examination: Visual inspection of bullet holes, including the examination of powder burns and tattooing around the wound, can provide clues about the firing distance. Microscopic examination of the bullet entry and exit holes helps forensic experts analyze the bullet's path and any associated marks.


Gunshot Residue (GSR) Examination

Gunshot residue examination is a vital forensic technique used to determine if a suspect has recently fired a firearm. GSR consists of microscopic particles expelled from the firearm during discharge, which can settle on the shooter’s hands, clothing, and nearby surfaces. Key methods for GSR analysis include:

  • Collection Techniques: GSR samples are typically collected using adhesive stubs, swabs, or vacuum devices from the suspect's hands, clothing, or other relevant surfaces. Proper collection is critical to avoid contamination.

  • Scanning Electron Microscopy (SEM): SEM is used to precisely identify GSR particles by their morphology and elemental composition. SEM can detect characteristic elements such as lead, barium, and antimony, which are commonly found in GSR. This technique provides high-resolution images and detailed chemical analysis, confirming the presence of GSR particles.

  • Energy Dispersive X-ray Spectroscopy (EDS): Often used in conjunction with SEM, EDS analyzes the elemental composition of particles, helping to distinguish GSR from other environmental contaminants.


Restoration of Erased Serial Numbers

Firearms with obliterated serial numbers pose a significant challenge in forensic investigations. Restoring these serial numbers can provide critical evidence linking a firearm to its owner. Various methods are used for serial number restoration:

  • Chemical Etching: This technique involves applying acidic or basic solutions to the metal surface where the serial number was located. The chemical reacts differently with the deformed metal areas (where the serial number was stamped) compared to the surrounding metal, revealing the obliterated digits.

  • Electrolytic Restoration: In this method, an electrolyte solution and an electric current are used to reverse the process of obliteration. The electric current causes the deformed areas to dissolve at a different rate, allowing the original serial number to reappear.

    • This is a very common method to remove rust from metallic surfaces.

  • Magnetic Particle Inspection: This non-destructive technique uses magnetic fields and ferromagnetic particles to reveal the serial number. The firearm is magnetized, and magnetic particles are applied to the surface. The particles accumulate in the areas of metal deformation, making the serial number visible under appropriate lighting conditions.

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