Pinoy Crim
JurisprudenceLaw EnforcementCriminalisticsCrime DetectionSociology of CrimesCorrectional Admin
Practice Exams

Module 7.9: Forensic Ballistics (Interior, Exterior, Terminal)

I. The Three Branches of Ballistics

The study of ballistics is traditionally divided into three distinct phases of a projectile's journey.

A. Interior (Internal) Ballistics

  • Scope: Covers everything that happens inside the firearm from the moment the firing pin strikes the primer until the bullet exits the muzzle.
  • Key Areas of Study:
    • The mechanism of firing.
    • The ignition of the primer and propellant (gunpowder).
    • The generation of gas pressure.
    • The movement of the bullet down the barrel.
    • The engraving of markings onto the bullet and cartridge case by the parts of the gun.
  • This is the most important branch for forensic firearms identification.

Ang Interior Ballistics ay tungkol sa lahat ng nangyayari INSIDE the firearm - mula sa pagpindot ng firing pin sa primer hanggang sa paglabas ng bala sa muzzle. Dito napag-aaralan: (1) firing mechanism, (2) pag-ignite ng primer at gunpowder, (3) gas pressure na nag-push sa bullet, (4) movement ng bullet sa loob ng barrel, at (5) ang engraving ng unique markings sa bullet at cartridge case - ITO ANG PINAKA-IMPORTANTE para sa forensic identification! Kaya ito ang most important branch ng ballistics for criminalists!

B. Exterior (External) Ballistics

  • Scope: Covers the flight of the bullet from the muzzle to the target.
  • Key Areas of Study:
    • The trajectory (path) of the bullet.
    • The effects of air resistance (drag) and gravity on the bullet's flight.
    • The bullet's velocity and energy.
    • Yaw and Tumble: The spinning and wobbling motion of the bullet in flight.
  • Forensic Relevance: Useful for reconstructing crime scenes, such as estimating the distance between the shooter and the target or determining the trajectory of a stray bullet.

C. Terminal Ballistics

  • Scope: Covers the behavior of the bullet upon impact with the target.
  • Key Areas of Study:
    • The bullet's penetration, perforation, and energy transfer to the target.
    • The nature and extent of the damage caused (wound ballistics in the case of a human target).
    • Ricochet (the bouncing of a bullet off a surface).
    • Bullet deformation and fragmentation.
  • Forensic Relevance: Essential for forensic pathologists in understanding the nature of gunshot wounds and for crime scene analysts in interpreting bullet holes and damage.

III. The Firearms Identification Process

  1. Collection of Evidence: An evidence bullet or cartridge case is recovered from the crime scene. A suspect firearm is also recovered.
  2. Test Firing: The firearms examiner fires the suspect firearm into a water tank or a box of cotton (a "bullet trap") to obtain a known "test" bullet and cartridge case that are undamaged.
  3. Microscopic Comparison: The examiner uses a comparison microscope.
    • This is essentially two microscopes connected by an optical bridge, allowing the examiner to view two objects side-by-side in the same field of view.
    • The examiner places the evidence bullet under one side and the test bullet under the other.
    • By rotating the bullets, the examiner tries to find a "match" in the unique pattern of striations. If a sufficient number of matching striations are found, a positive identification is made. The same process is used for comparing cartridge cases.

Ang process ng firearms identification ay ganito: (1) Collection - kukunin ang evidence bullet/cartridge case mula sa crime scene at suspect firearm; (2) Test Firing - pututukan ng firearms examiner ang suspect gun into a water tank o cotton box para makakuha ng "test" bullet/cartridge na undamaged; (3) Microscopic Comparison - gamit ang comparison microscope (dalawang microscopes na connected by optical bridge), titingnan side-by-side ang evidence bullet at test bullet. Iroro-rotate ang bullets para hanapin ang matching striations. Pag sufficient matches ang nahanap - POSITIVE IDENTIFICATION! Same process para sa cartridge cases.

Board Exam Tip: The comparison microscope is the single most important instrument for a firearms examiner. Remember it!

Conclusion

Forensic Ballistics is a powerful tool that can provide a definitive link between a firearm and a crime. The process relies on the fundamental principle that every firearm, through the random imperfections of its manufacturing, is unique. By analyzing the microscopic striations engraved on a bullet as it travels down the barrel, and the unique impressions left on a cartridge case, a skilled examiner can identify the "fingerprint" of a gun, providing crucial evidence for the criminal justice system.

Introduction

Forensic Ballistics is the science of firearms and ammunition, specifically as it pertains to criminal investigations. It is the discipline concerned with determining if a bullet, cartridge case, or other ammunition component was fired from a specific firearm. This is possible because, much like a fingerprint, every firearm has unique characteristics that it imparts onto the ammunition it fires. This module will break down the field of ballistics into its three main branches and detail the process of firearms identification.

Key Learning Objectives:

  • Define Forensic Ballistics and its purpose.
  • Differentiate between the three branches of ballistics: Interior, Exterior, and Terminal.
  • Explain how a firearm leaves unique markings (striations) on bullets and cartridge cases.
  • Describe the function of the comparison microscope in firearms identification.
  • Understand the role of automated database systems like IBIS.

II. The Basis of Firearms Identification

The ability to match a bullet to a specific gun is based on the fact that the manufacturing process leaves microscopic imperfections on the internal parts of the firearm. These imperfections are unique to each gun.

A. The Barrel and Rifling

  • The inside of a gun barrel is not smooth. It contains a set of spiral grooves called rifling.
  • Purpose of Rifling: The rifling grips the bullet as it travels down the barrel, causing it to spin. This spinning motion (like a quarterback throwing a spiral) provides gyroscopic stability, making the bullet more accurate.
  • Rifling Characteristics:
    • Lands: The raised portions between the grooves.
    • Grooves: The recessed portions.
    • Caliber: The diameter of the barrel, measured from land to land.
    • Twist: The direction of the spiral (e.g., right-hand twist or left-hand twist).
  • Class Characteristics: The number of lands and grooves, and the direction of twist, are class characteristics common to a particular make and model of firearm (e.g., a Glock 19 has 6 grooves with a right-hand twist).

B. The Creation of Striations (Individual Characteristics)

  • During manufacturing, the tools used to cut the rifling leave microscopic scratches and imperfections inside the barrel. These imperfections are random and unique to each barrel.
  • As a soft lead or copper-jacketed bullet is forced down the barrel under immense pressure, the rifling engraves both the class characteristics (lands and grooves) and the individual characteristics (the unique microscopic scratches) onto its surface.
  • These fine, parallel scratches are called striations. It is the unique pattern of these striations that allows an examiner to match a bullet back to a single, specific firearm.

Eto ang magic ng firearms identification! Sa manufacturing process, ang tools na ginagamit para mag-cut ng rifling ay nag-iiwan ng microscopic scratches and imperfections sa loob ng barrel - ito ay UNIQUE sa bawat baril, tulad ng fingerprint! Pag pumaputok ang baril, ang soft bullet (lead o copper-jacketed) ay napipilitang dumaan sa barrel under immense pressure. Habang dumadaan, ang rifling ay nag-eengrave ng dalawang bagay sa bullet: (1) class characteristics - lands and grooves (common sa lahat ng same model); (2) individual characteristics - yung unique microscopic scratches o striations. Ang pattern ng striations ay parang "fingerprint of the gun" - pwedeng i-match ang bullet back to EXACTLY ONE SPECIFIC FIREARM!

Board Exam Tip: Striations = microscopic scratches = individual characteristics = unique to ONE gun. This is the BASIS of firearms identification!

C. Cartridge Case Markings

  • The firearm also leaves unique markings on the cartridge case.
    • Firing Pin Impression: The mark left by the firing pin on the primer cap.
    • Breechface Markings: The pressure of the explosion slams the back of the cartridge case against the breechface (the rear wall of the firearm's chamber), imprinting any imperfections from the breechface onto the cartridge.
    • Ejector and Extractor Marks: In semi-automatic and automatic firearms, the extractor hook and the ejector leave unique marks as they pull and push the spent cartridge out of the chamber.

IV. Automated Identification Systems

  • IBIS (Integrated Ballistics Identification System): A computerized system that automates the comparison of ballistics evidence.
  • How it Works: IBIS does not make a conclusive match. Instead, it captures digital images of the markings on bullets and cartridge cases and stores them in a database. It then compares the images of evidence from a crime scene to the database and produces a "shortlist" of likely matches.
  • The Role of the Examiner: A human firearms examiner must then physically pull the evidence from the shortlisted items and perform a final, conclusive comparison using a traditional comparison microscope. IBIS is a screening tool, not a replacement for the expert examiner.