Firearms Evidence and Cartridge Components
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Firearms Evidence and Cartridge Components

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Questions and Answers

What is the purpose of rifling in a barrel?

  • To increase the speed of the bullet.
  • To create a smooth surface for the bullet.
  • To stabilize the bullet's trajectory through spinning. (correct)
  • To reduce recoil when firing.

    • Which characteristic is NOT considered a class characteristic of firearms?

  • Individual scratches on the barrel (correct)
  • Direction of twist
  • Caliber
  • Number of lands and grooves

    • How is the caliber of a firearm expressed?

  • As the length of the firing pin.
  • As bore or groove diameter in inches. (correct)
  • As the maximum bullet weight it can fire.
  • As a percentage of the barrel length.

    • What refers to the impressions on a fired bullet as a result of rifling?

    <p>Land and groove impressions</p> Signup and view all the answers

    What could indicate a family of firearms?

    <p>Same caliber and number of lands and grooves.</p> Signup and view all the answers

    What type of firearm is characterized as having no rifling in its barrel?

    <p>Shotgun</p> Signup and view all the answers

    Which characteristic is a result of firing a bullet through a barrel?

    <p>The land impressions and groove impressions on the bullet.</p> Signup and view all the answers

    What should be avoided when estimating the caliber of a bullet?

    <p>Allowing for potential distorting of the bullet.</p> Signup and view all the answers

    What is the first safety consideration when handling firearms?

    <p>Treat every firearm as if it is loaded</p> Signup and view all the answers

    When documenting firearms evidence, what should you NOT do?

    <p>Manipulate the firearm immediately for a better angle</p> Signup and view all the answers

    What is the correct procedure for unloading a revolver?

    <p>Mark the cylinder and record the position of each round</p> Signup and view all the answers

    Which step should be taken first when unloading autoloading firearms?

    <p>Remove the magazine from the firearm</p> Signup and view all the answers

    What should you do if you find a jammed firearm?

    <p>Ask someone experienced for help</p> Signup and view all the answers

    Which detail is NOT vital to record when identifying a firearm?

    <p>Condition of the ammunition</p> Signup and view all the answers

    After examining evidence such as fingerprints, what is crucial before unloading a firearm?

    <p>Unloading should be done safely and carefully</p> Signup and view all the answers

    What should be included when packaging evidence from firearms?

    <p>Package each item separately, indicating its position</p> Signup and view all the answers

    What is the primary reason for treating all firearms as though they are loaded?

    <p>To prevent accidents involving unloaded firearms</p> Signup and view all the answers

    Which component is NOT part of a firearm cartridge?

    <p>Wad</p> Signup and view all the answers

    Which type of cartridge is characterized by having the priming compound encased around the rim?

    <p>Rimfire</p> Signup and view all the answers

    What is the shape of most centerfire rifle cartridges?

    <p>Bottlenecked</p> Signup and view all the answers

    What is the primary component that influences the burning rate of propellant grains?

    <p>Shape of the grains</p> Signup and view all the answers

    Which of the following firearms is most commonly involved in criminal cases?

    <p>Revolvers</p> Signup and view all the answers

    Which part of a shotshell is responsible for containing the projectiles?

    <p>Wad</p> Signup and view all the answers

    What is a common misconception about firearm cases in educational settings?

    <p>Cases are often called shells</p> Signup and view all the answers

    What should be done if a loaded handgun is transported by mail?

    <p>It must be unloaded and securely packaged.</p> Signup and view all the answers

    When bullets are embedded in wood or plaster, what is the recommended recovery method?

    <p>Cut or saw out the wall portion containing the bullet.</p> Signup and view all the answers

    How should ejected cartridge cases be handled at a crime scene?

    <p>Each cartridge case should be packaged separately.</p> Signup and view all the answers

    What should be done if live shot shells or cartridges are found at a crime scene?

    <p>All ammunition should be submitted for examination.</p> Signup and view all the answers

    What is crucial to record regarding the location of cartridge cases?

    <p>Measure and sketch the position of all ejected cartridge cases.</p> Signup and view all the answers

    If shot pellets are embedded, what should be the recovery approach?

    <p>Process them as embedded bullets.</p> Signup and view all the answers

    What is the preferred method of delivering firearms evidence to the lab?

    <p>Personal delivery is preferred.</p> Signup and view all the answers

    What device should be used to remove a bullet from a deceased person?

    <p>Rubber-tipped or plastic forceps.</p> Signup and view all the answers

    What components are included in gunshot residues (GSR)?

    <p>Components from the primer, powder, projectile material, and products of their combustion</p> Signup and view all the answers

    Which method analyzes chemical extracts specifically for barium and antimony?

    <p>Atomic Absorption analysis (AA)</p> Signup and view all the answers

    How long can gunshot residues remain on a living person after discharge?

    <p>Several hours</p> Signup and view all the answers

    What should be done immediately after collecting GSR samples from a subject?

    <p>The investigator should wash their hands and put on gloves</p> Signup and view all the answers

    What is the consequence of using plastic bags on a living subject for GSR collection?

    <p>It will destroy any residues present due to sweat production</p> Signup and view all the answers

    Which step is NOT part of the procedure for GSR collection using a metal disc?

    <p>Wash hands after collecting samples</p> Signup and view all the answers

    What type of firearm will typically produce the most gunshot residue?

    <p>Cheaply made revolvers</p> Signup and view all the answers

    What is advised to do if hands cannot be processed right away for GSR?

    <p>Place new, clean, brown paper bags over the hands</p> Signup and view all the answers

    Study Notes

    Firearms Evidence

    • Firearms evidence is commonly encountered in crimes against persons, including homicide, assault, and robbery, as well as other offenses like burglary, rape, and narcotics violations.
    • Handguns, including revolvers and semi-automatic pistols, are the most prevalent firearms involved in criminal cases; however, long arms like shotguns and rifles are also involved.
    • Firearms evidence typically includes fired and unfired cartridges, gunshot residue on targets, and discharge residues on the hands of individuals who have fired or handled a discharged firearm.

    Cartridge Components

    • Cartridges consist of a cartridge case, primer, propellant (gunpowder), and bullet or projectile, all of which can become physical evidence in a shooting case.

    Cartridge Types

    • Rimfire (RF) cartridges have the priming compound encased around the rim.
    • Centerfire (CF) cartridges have the priming compound encased as a central primer and may have a rimmed, rimless, or semi-rimmed cartridge case.
    • The headstamp identifies the manufacturer and cartridge type.

    Cartridge Shapes

    • Cartridge cases come in three general shapes: straight, tapered, and bottlenecked.
    • Most .22 rimfire cartridges and centerfire cartridges have straight cases.
    • Most centerfire rifle cartridges have a bottlenecked shape, while tapered cases are largely obsolete.

    Rifled Barrels

    • Rifled barrels are named for the "rifling" produced in the bore of the barrel, which consists of lands (raised areas) and grooves (scraped out or compressed down areas).
    • The rifling twists to make the bullet spin, stabilizing its flight.
    • Shotguns lack rifling in their barrels and are considered smoothbore weapons.

    Class Characteristics of Firearms

    • Class characteristics of firearms include caliber, number of lands and grooves, width of lands and grooves, and direction of twist (including rate of twist). These characteristics can be used to establish a "family" of firearms that share the same make and model.

    Caliber

    • Caliber is expressed as bore diameter (d) or groove diameter (D) and is measured in either hundreds or thousands of an inch.
    • Sometimes, the barrel diameter may be different from the caliber; for example, .38 Special has a bore of .36 inches.

    Class Characteristics of Fired Bullets

    • Class characteristics of fired bullets include caliber, number of lands and grooves, and direction of twist.
    • These characteristics are a direct result of the barrel's rifling being impressed into the bullet's circumference during discharge.
    • The impressions on the bullet are referred to as land impressions and groove impressions.

    Fired Cartridge Cases

    • Fired cartridge cases exhibit an impression of the breech face, an ejector mark, override and gouge marks from the extractor, and chamber striations produced by the forced removal from the chamber.
    • They also have a firing pin impression.

    Lab Examinations of Firearms Evidence

    • Lab examinations of firearms evidence often include firearm identification, muzzle-to-target distance determinations, gunshot residue identifications, weapon functionality examinations, and bullet trajectory and/or sequence of firing determinations.

    Collection of Firearms Evidence

    • Safety is the paramount consideration when handling firearms evidence; always treat any firearm as though it is loaded.
    • Never point a firearm at anyone, and seek assistance if you are uncomfortable or unfamiliar with the firearm.

    Note-taking and Evidence Marking

    • Document the firearm's location and condition, including whether it is loaded or unloaded, if the hammer is cocked, and if the safety is on or off.
    • Sketch the area, showing the location of all evidence items.
    • Photograph the firearm before moving it, unless there is an emergency.
    • Unload the firearm safely and record ammunition found in the chamber, loaded magazine (in semi-automatics), or cartridge cases/ammunition (in revolvers). Identify the weapon by recording the make, model, and serial number on a tag tied to the trigger guard.

    Unloading Revolvers

    • Mark the cylinder to indicate the chamber aligned with the barrel.
    • Record the position of each round in the cylinder in your notes.
    • Package each round separately, indicating the chamber location on the evidence packaging.

    Unloading Autoloading Firearms

    • Point the gun down.
    • Release the magazine.
    • Pull back the slide to release the ammunition in the chamber.
    • Package the firearm and magazine separately; do not remove ammunition from the magazine.

    Collection of Firearms Evidence (Water)

    • If a weapon is found in water, place it in a container with the same water covering the weapon.
    • Rapid rusting will occur if the weapon is removed from the water and allowed to partially dry.

    Transporting to the Lab

    • Personal delivery is preferred, and loaded handguns can be transported in specially constructed boxes that hold the firearm securely in place.
    • If a firearm must be mailed, it must be unloaded, securely packaged, and clearly marked. Live ammunition cannot be shipped via US mail.

    Recovery of Fired Ammunition Components

    • Embedded bullets: sketch the location of the bullet hole, cut or saw out the wall portion containing the bullet (do not dig it out).
    • Bullets embedded in deceased persons: X-ray the body, remove the bullet with rubber-tipped or plastic forceps or fingers, and package the bullet as is for examination at the lab.
    • Cartridge cases: sketch and measure their position, package each one separately.
    • Shot wads (shotguns): travel behind the shot pellets and are collected using the same method as ejected cartridge cases.
    • Shot pellets : process embedded pellets similarly to embedded bullets; otherwise, dig them out using rubber-tipped or plastic tweezers.
    • Live shot shells or cartridges: submit all found ammunition related to the case.
    • Boxes of ammunition: submit boxes of ammunition for testing in the lab.

    Gunshot Residues (GSR)

    • GSR is a result of the discharge of a firearm. It includes components from the primer, powder, projectile material, and products of their combustion.
    • The amount of GSR varies based on the type of firearm, ammunition, and conditions of discharge.
    • Cheaply made revolvers produce the most amount of GSR, and the use of shotguns or rifles can produce GSR on the shooter's cheek.

    Gunshot Residue Analysis Methods

    • Several methods are used for gunshot residue analysis, including neutron activation analysis (NAA), atomic absorption analysis (AA), and scanning electron microscopy/energy dispersive x-ray analysis (SEM/EDX).

    Collection of Gunshot Residues

    • GSR can be found on a living person for several hours after firing, though it is considered lost after 6 hours.
    • Process the subject’s hands as soon as possible; the subject should not be allowed to wash or rub their hands before sampling, as GSR can be easily removed.
    • If hands cannot be processed immediately, place new, clean brown paper bags over the subject's hands and tape the bag to the wrist. Never use plastic bags on a live subject, as sweat can destroy residues; plastic bags can be used on deceased subjects.
    • Investigators should wash their hands and put on gloves before collecting GSR.

    GSR Collection Procedures

    • Metal discs: use these before swabbing for AA analysis.
      • Wash your hands and wrists, wear provided gloves.
      • Remove the protective cover.
      • Press the sticky portion of the disc lightly onto the hand repeatedly until it is no longer sticky.
      • Seal the disc in the provided container.
      • Repeat for other areas.
    • Swabs: use these for AA analysis.
      • Put on gloves before touching anything from the kit.
      • Add nitric acid to the acid control swabs and place them back in the container.
      • Remove one swab from the "right back" tube and moisten it with 5% nitric acid solution.

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    Description

    This quiz explores the role of firearms evidence in criminal cases, particularly in violent crimes like homicide and assault. It delves into the composition of cartridges, including their various components and types. Gain insights into how firearms and their evidence contribute to criminal investigations.

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