Forensic Ballistics Review Questions 1
Forensic Ballistics Review Questions 1
1. In forensic ballistics, what is the term for the raised area between the grooves inside a firearm's barrel?
A. Caliber
B. Land
C. Rifling
D. Smoothbore
Answer: B
Lands are the raised portions between grooves inside a rifled barrel.
2. Which term refers to the internal diameter of a firearm's barrel, typically measured between opposing lands, or the diameter of the ammunition designed for it?
A. Caliber
B. Land
C. Rifling
D. Smoothbore
Answer: A
Caliber refers to the bore diameter (commonly measured between opposing lands) or the cartridge/bullet size.
3. During a forensic investigation, a ballistics expert examines a fired bullet and notices distinct impressions left by the raised ridges inside the gun barrel. What are these specific raised helical structures called?
A. Caliber
B. Land
C. Rifling
D. Smoothbore
Answer: B
The raised helical ridges that impress the bullet are called lands.
4. What is the name for the overall system of spiral grooves and ridges machined into the interior of a firearm barrel to impart a stabilizing spin on a bullet?
A. Caliber
B. Land
C. Rifling
D. Smoothbore
Answer: C
Rifling is the overall system of spiral lands and grooves that spins the bullet.
5. Which type of firearm design features a completely flat, ungrooved interior barrel surface that does not impart a spin on the projectile?
A. Caliber
B. Land
C. Rifling
D. Smoothbore
Answer: D
A smoothbore barrel lacks rifling and does not impart spin.
6. During a forensic examination of a fired cartridge case recovered from a crime scene, the ballistician observes a distinct toolmark on the rim or the groove of the casing. This mark is left when the mechanical claw of the firearm pulls the spent shell out of the breech chamber after firing. Which of the following marks is being described?
A. Firing Pin Mark
B. Extractor Mark
C. Ejector Mark
D. Shearing Mark
Answer: B
Extractor marks are produced when the extractor pulls the cartridge case from the chamber.
7. A suspect weapon is test-fired in a laboratory. Upon examining the base of the fired cartridge case, the examiner notes a deep indentation directly in the center of the primer cup, caused by the strike that ignited the priming mixture. What type of mark is this?
A. Firing Pin Mark
B. Extractor Mark
C. Ejector Mark
D. Shearing Mark
Answer: A
The indentation in the primer caused by the firing pin is a firing pin impression/mark.
8. In a homicide investigation, a spent cartridge case is found with a clear, localized scuff mark on the rear face of the head, typically located opposite the extractor mark. This mark is created when the cartridge is pushed forward and flipped out of the firearm's ejection port by a protruding metal component. This is known as a/an:
A. Firing Pin Mark
B. Extractor Mark
C. Ejector Mark
D. Shearing Mark
Answer: C
Ejector marks are made when the ejector strikes the case and expels it from the firearm.
9. While examining a cartridge case fired from a semi-automatic pistol, a forensic ballistics expert notices a shaved or striated mark on the primer. This happens when the firing pin protrudes from the breech face as the barrel drops down during the unlocking cycle, causing the metal to scrape. This specialized toolmark is called a:
A. Firing Pin Mark
B. Extractor Mark
C. Ejector Mark
D. Shearing Mark
Answer: D
Primer shearing marks are striated marks caused during unlocking as metal is scraped around the firing pin aperture.
10. Which of the following marks on a cartridge case is primarily produced by the rearward motion of the casing pushing against the ejector block or pin, effectively forcing the empty shell to spin out of the gun?
A. Firing Pin Mark
B. Extractor Mark
C. Ejector Mark
D. Shearing Mark
Answer: C
11. Which part of a cartridge contains the projectile?
A. Primer
B. Bullet
C. Powder
D. Rim
Answer: B. The bullet is the projectile that leaves the barrel and travels toward the target.
12. Which part of the ammunition ignites the propellant when struck by the firing pin?
A. Case
B. Bullet
C. Primer
D. Rim
Answer: C. The primer contains a shock-sensitive compound that ignites when struck by the firing pin, which in turn ignites the propellant.
13. What part of the cartridge holds all the other components together?
A. Case
B. Primer
C. Bullet
D. Powder
Answer: A. The case (or cartridge case) contains the primer, propellant, and bullet, holding them together as a complete cartridge.
14. Which component produces the expanding gases that propel the bullet?
A. Primer
B. Rim
C. Propellant powder
D. Bullet jacket
Answer: C. The burning propellant powder generates high-pressure gases that drive the bullet down the barrel.
15. In centerfire ammunition, the primer is located at the:
A. Tip of the bullet
B. Side of the case
C. Center of the base
D. Neck of the case
Answer: C. In centerfire cartridges, the primer is seated in the center of the cartridge base (head).
16. Which part of a cartridge travels through the barrel toward the target?
A. Case
B. Primer
C. Bullet
D. Powder
Answer: C. Only the bullet exits the barrel; the case remains in the firearm.
17. The groove near the base of a cartridge case is primarily used for:
A. Holding the primer
B. Bullet expansion
C. Extraction by the extractor
D. Igniting the powder
Answer: C. The extractor groove allows the firearm's extractor to grip and remove the spent cartridge case from the chamber.
18. The neck of a bottleneck cartridge case serves to:
A. Hold the bullet securely
B. Contain the primer
C. Catch the extractor
D. Increase recoil
Answer: A. The neck grips the bullet firmly to keep it properly seated before firing.
19. Which sequence correctly describes the firing process of a cartridge?
A. Powder → Primer → Bullet
B. Primer → Powder → Bullet
C. Bullet → Primer → Powder
D. Bullet → Powder → Primer
Answer: B. The firing pin strikes the primer, which ignites the powder, producing gases that propel the bullet.
20. Which part of the cartridge case supports the primer in centerfire ammunition?
A. Mouth
B. Neck
C. Head
D. Shoulder
Answer: C. The head of the cartridge case contains the primer pocket and provides support for the primer.
21. These are firearm characteristics determined by microscopic random imperfections produced during manufacture, wear, tear, rust, and abuse, which serve as the basis for positive identification:
A. Class characteristics
B. Accidental characteristics
C. Individual characteristics
D. Manufacturing specifications
Answer: C. Individual characteristics
Unlike class characteristics (e.g., caliber, number of lands and grooves), individual characteristics are random microscopic imperfections unique to a single firearm that allow examiners to positively identify a fired bullet or shell as having come from that specific weapon.
22. Microscopic fine parallel scratches etched onto the surface of a bullet as it passes through the rifled barrel of a gun are called:
A. Land impressions
B. Striations
C. Skid marks
D. Wipe marks
Answer: B. Striations
Striations (or striae) are microscopic tool marks/scratches produced inside the barrel during machining or through wear and tear. They transfer onto the bullet as individual characteristics.
23. Which tool or instrument is primarily used by forensic ballisticians to observe individual characteristics by comparing an evidence bullet alongside a test-fired bullet?
A. Stereoscopic Microscope
B. Comparison Microscope
C. Scanning Electron Microscope
D. Compound Microscope
Answer: B. Comparison Microscope
Explanation: Magnification to match striations and individual tool marks.
24. Which type of mark may be left on a cartridge case as it is stripped from the magazine and fed into the chamber of a firearm?
A. Firing pin impression
B. Extractor mark
C. Magazine lip mark
D. Breechface mark
Answer: C. Magazine lip mark
A magazine lip mark may be produced when the cartridge case contacts the lips of the magazine as the cartridge is stripped from the magazine and fed into the chamber. Such marks may provide useful microscopic characteristics in firearm examination.
25. Marks impressed upon the head/base of a cartridge case when the expanding gas forces the cartridge backward against the rear wall of the chamber are called:
A. Ejector marks
B. Extractor marks
C. Breechface marks
D. Firing pin impressions
Answer: C. Breechface marks
Explanation: Microscopic tool marks on the soft primer and base of the cartridge.
26. Striations found on the sides of a bullet caused by the lands and grooves of a worn or defective barrel are classified as what type of characteristic?
A. Individual characteristic
B. Class characteristic
C. Temporary characteristic
D. Chemical characteristic
Answer: A. Individual characteristic
While the broad dimensions of lands and grooves are class characteristics, the minute striations inside them caused by tool wear, erosion, or corrosion are individual characteristics.
27. What unique mark is left on the rim or groove of a fired cartridge case when the claw-like mechanism pulls it out of the chamber?
A. Ejector mark
B. Extractor mark
C. Chamber mark
D. Firing pin mark
Answer: B. Extractor mark
The extractor is the mechanism that hooks onto the rim/groove of the cartridge to withdraw it from the chamber after firing, leaving distinct individual tool marks.
28. Which of the following is considered a CLASS characteristic rather than an INDIVIDUAL characteristic of a firearm barrel?
A. Microscopic tool marks on the rifling land
B. Rust pitting inside the bore
C. Direction of twist (Right or Left)
D. Gouges caused by improper cleaning methods
Answer: C. Direction of twist (Right or Left)
Direction of twist, caliber, and the number/width of lands and grooves are determined before manufacture and are shared by all weapons of the same make and model (Class characteristics). The rest are individual imperfections.
29. A mark left on the head of a cartridge case when it is forcibly flipped out of the firearm's ejection port by a small metal projection is called a/an:
A. Extractor mark
B. Ejector mark
C. Shearing mark
D. Firing pin indent
Answer: B. Ejector mark
The ejector strikes the base or side of the fired cartridge case to kick it out of the weapon, leaving an individual contact mark.
30. Why are individual characteristics essential in forensic ballistics during court proceedings?
A. They identify the caliber and weapon type used in the crime.
B. They determine the distance from which the gun was fired.
C. They provide a basis for associating a fired bullet or cartridge case with a particular firearm.
D. They reveal the manufacturer and year of production of the gun.
Answer: C.
They provide a basis for associating a fired bullet or cartridge case with a particular firearm.
Individual characteristics are unique, like fingerprints; they provide the scientific basis for an expert witness to testify that a specific bullet or shell was fired from one specific gun.
31. Which characteristic primarily distinguishes a handgun from a long gun?
A. Caliber size
B. Barrel length and overall design for one-handed vs. shoulder-fired use
C. Magazine capacity
D. Type of primer used
Correct Answer: B
Explanation: Handguns (pistols and revolvers) are designed to be fired using one or both hands without shoulder support, whereas long guns (rifles and shotguns) feature longer barrels and stocks designed to be braced against the shoulder.
32. A firearm with a smooth-bore interior barrel is typically classified as a:
A. Rifle
B. Handgun
C. Shotgun
D. Submachine gun
Correct Answer: C
Explanation: Shotguns generally feature a smooth interior barrel to fire multiple pellets (shot) efficiently, unlike rifles and handguns, which feature helical grooves (rifling) to impart spin on a single bullet.
33. What action type requires the shooter to manually cycle a sliding mechanism back and forth to eject a spent casing and load a new cartridge?
A. Lever action
B. Bolt action
C. Pump action
D. Break action
Correct Answer: C
Explanation: Pump-action (or slide-action) firearms utilize a sliding fore-end moved manually back and forth by the shooter to clear the chamber and feed the next round.
34. How is a semi-automatic firearm defined?
A. Fires continuously as long as the trigger is held down
B. Fires one round per trigger pull and automatically reloads the chamber
C. Requires manual cocking of the hammer before every single shot
D. Fires multiple projectiles simultaneously with one trigger pull
Correct Answer: B
Explanation: Semi-automatic firearms use the energy from a fired cartridge to automatically eject the empty casing and chamber a new round, requiring a separate pull of the trigger for each subsequent shot.
35. What feature distinguishes a revolver from a standard semi-automatic pistol?
A. Revolvers use detachable box magazines
B. Revolvers have a rotating cylinder containing multiple chambers
C. Revolvers are always fully automatic
D. Revolvers do not have a trigger guard
Correct Answer: B
Explanation: Revolvers hold cartridges in a revolving cylinder that indexes a new chamber into alignment with the single barrel for each shot, whereas semi-automatic pistols typically feed cartridges from a magazine into a single fixed chamber.
36. Which term describes helical grooves cut into the inside of a firearm's barrel?
A. Choke
B. Rifling
C. Caliber
D. Gauge
Correct Answer: B
Explanation: Rifling consists of spiral grooves inside the bore that spin the bullet during flight, improving aerodynamic stability and accuracy.
37. In shotgun classification, what unit of measurement is typically used to specify bore diameter?
A. Caliber
B. Millimeters
C. Gauge
D. Grains
Correct Answer: C
Explanation: Shotgun barrels (except for the .410) are measured in gauge, historically determined by the number of solid lead balls of bore diameter needed to equal one pound. (e.g., a 12-gauge requires 12 lead balls to equal 1 lb).
38. Under standard legal and technical definitions, what makes a firearm "fully automatic"?
A. Reloading the magazine without manual intervention
B. Firing continuous rounds with a single continuous pull of the trigger
C. Having an integrated optical sight
D. Using high-capacity magazines
Correct Answer: B
Explanation: Fully automatic firearms (machine guns) continue to load, fire, and cycle cartridges repeatedly for as long as the trigger is held back until the ammunition is depleted or the trigger is released.
39. What type of firearm action hinges open at the breach to allow manual loading and unloading of cartridges directly into the chamber?
A. Break action
B. Bolt action
C. Revolving action
D. Blowback action
Correct Answer: A
Explanation: Break-action (or hinge-action) firearms pivot open on a hinge pin near the breech, exposing the rear of the barrels for direct manual loading and extraction.
40. How does rimfire ammunition differ from centerfire ammunition in firearm classification?
A. Rimfire cartridges can be reloaded multiple times
B. Rimfire primer compound is located inside the outer rim of the cartridge base
C. Rimfire is reserved exclusively for military rifles
D. Rimfire cartridges lack gunpowder
Correct Answer: B
Explanation: Rimfire ammunition places the sensitive priming compound inside the hollow rim of the cartridge case, which is struck directly by the firing pin. Centerfire ammunition uses a separate, self-contained primer cup seated in the middle of the casing head.
41. Which part of the ammunition contains the primer, powder, and bullet together?
A. Projectile
B. Casing
C. Rim
D. Primer
Correct Answer: B. Casing
Explanation: The casing (or cartridge case) is the container that holds all the component parts of a round of ammunition together in a single unit.
42. What is the actual object that exits the barrel when a firearm is discharged?
A. Cartridge
B. Primer
C. Bullet
D. Shell
Correct Answer: C. Bullet
Explanation: The bullet (or projectile) is the component located at the front of the casing that is expelled through the barrel toward the target.
43. Which component contains a pressure-sensitive chemical compound that ignites the main powder charge?
A. Casing
B. Primer
C. Wad
D. Flash hole
Correct Answer: B. Primer
Explanation: The primer is a small chemical cap at the base of the cartridge. When struck by the firing pin, it creates a small flame that ignites the main propellant.
44. What component of a cartridge burns rapidly to produce expanding gases that propel the bullet?
A. Propellant
B. Lead core
C. Primer composition
D. Anvil
Correct Answer: A. Propellant
Explanation: Gunpowder (or propellant) burns rapidly within the sealed casing, expanding into gas and creating high pressure to propel the bullet out of the barrel.
45. In shotgun shells, what part separates the powder charge from the shot or slug?
A. Rim
B. Wad
C. Hull
D. Anvil
Correct Answer: B. Wad
Explanation: The wad acts as a partition in a shotgun shell, sealing gases behind the shot or slug and cushioning the projectiles during firing.
46. What is the small opening at the base of the casing through which the primer's spark travels to the powder?
A. Flash hole
B. Primer pocket
C. Extractor groove
D. Extraction rim
Correct Answer: A. Flash hole
Explanation: The flash hole connects the primer pocket to the main casing interior, allowing the primer's spark to reach and ignite the gunpowder.
47. Which part of a jacketed bullet surrounds and encloses the softer core?
A. Jacket
B. Rim
C. Casing
D. Anvil
Correct Answer: A. Jacket
Explanation: The jacket is the outer covering of a jacketed bullet, commonly made of copper or a copper alloy. It surrounds the core, which is commonly made of lead, and helps the bullet maintain its shape during firing.
48. Which feature of a rimless cartridge case provides a groove for the extractor to engage?
A. Flash hole
B. Extractor groove
C. Casing mouth
D. Primer pocket
Correct Answer: B. Extractor groove
Explanation: The extractor groove is the recessed groove near the base of a rimless cartridge case. The firearm's extractor engages this groove to pull the fired cartridge case from the chamber.
49. What part of a shotgun shell holds the components together, functioning similarly to a centerfire cartridge case?
A. Hull
B. Choke
C. Primer cup
D. Slug
Correct Answer: A. Hull
Explanation: The hull is the outer plastic or paper tube (attached to a brass base) that serves as the casing for a shotgun shell.
50. In centerfire primer cups, what solid metal surface does the primer compound get crushed against to detonate?
A. Flash hole
B. Anvil
C. Rim
D. Ogive
Correct Answer: B. Anvil
The anvil is the internal metal component of a primer against which the primer compound is crushed when struck by the firing pin. This crushing action initiates the primer and produces hot gases that ignite the propellant.
51. Which branch of ballistics focuses on the events occurring from the moment the firing pin strikes the primer until the projectile exits the barrel?
A. External ballistics
B. Intermediate ballistics
C. Terminal ballistics
D. Internal ballistics
Correct answer: D.
Internal ballistics covers all mechanical and chemical phenomena taking place inside the firearm before the bullet leaves the muzzle. Properly describes events from primer ignition until the projectile leaves the muzzle.
52. The study of the projectile's behavior in the transitional region where high-pressure propellant gases expand past the muzzle is known as:
A. Internal ballistics
B. External ballistics
C. Intermediate ballistics
D. Terminal ballistics
Answer: C.
Intermediate (or transition) ballistics studies the short distance outside the muzzle where escaping gases continue to influence bullet flight. Correctly describes the transition immediately outside the muzzle, while propellant gases still affect the projectile.
53. Which factor is primarily analyzed under external ballistics?
A. Ignition delay
B. Muzzle blast flash
C. Cavitation in tissue
D. Aerodynamic drag
Answer: D.
Aerodynamic drag, gravity, wind, and gyroscopic drift are central elements of external ballistics during free flight. Drag is a classic external-ballistics factor.
54. Analyzing bullet tissue deformation, energy transfer, and wounding mechanisms upon impact falls under which branch?
A. Intermediate ballistics
B. Terminal ballistics
C. External ballistics
D. Internal ballistics
Answer: B.
Terminal ballistics deals specifically with bullet dynamics, penetration, fragmentation, and energy deposition in targets.
55. What primary internal ballistic parameter limits maximum bullet acceleration inside a rifle barrel?
A. Target yield strength
B. Ballistic coefficient
C. Peak chamber pressure
D. Coriolis effect
Answer: C.
Peak chamber pressure is a major internal-ballistic factor because it determines the force available to accelerate the projectile and must remain within the firearm's safe pressure limits.
56. Magnus effect and gyroscopic precession are critical considerations within which discipline?
A. External ballistics
B. Intermediate ballistics
C. Internal ballistics
D. Terminal ballistics
Answer: A
Spinning projectiles encounter crosswinds and air resistance that induce Magnus forces and gyroscopic stability issues during atmospheric trajectory. Magnus effects and gyroscopic behavior are primarily studied during projectile flight through the atmosphere.
57. The formation of a 'permanent cavity' and a 'temporary cavity' is a core subject of:
A. Intermediate ballistics
B. Terminal ballistics
C. Internal ballistics
D. External ballistics
Answer: B
Permanent and temporary cavitation describe kinetic energy transfer and tissue displacement upon impact.
58. A suppressor or flash hider primarily modifies factors belonging to which branch of ballistics?
A. External ballistics
B. Terminal ballistics
C. Internal ballistics
D. Intermediate ballistics
Answer: D.
Muzzle attachments like suppressors alter the expansion, temperature, noise, and pressure wave of gases as the projectile exits.
59. How does rifling twist rate in a gun barrel connect internal ballistics to external ballistics?
A. It increases terminal expansion by softening bullet jackets
B. It eliminates intermediate muzzle pressure completely
C. It imparts angular velocity internally to ensure gyroscopic stability externally
D. It regulates chemical burn rate to reduce external noise
Answer: C
Engraving into the bullet internally gives it spin, which prevents tumbling during external atmospheric flight. Rifling imparts spin while the projectile is in the barrel, contributing to gyroscopic stability during flight.
60. Which branch of ballistics primarily examines bullet construction and its effects on penetration, expansion, and fragmentation after striking a target?
A. Intermediate ballistics
B. Terminal ballistics
C. Internal ballistics
D. External ballistics
Answer: B.
Internal ballistics → events inside the firearm before the projectile exits.
Intermediate ballistics → the transition immediately after muzzle exit, particularly the continuing effects of propellant gases.
External ballistics → projectile flight through the atmosphere.
Terminal ballistics → projectile behavior and effects upon striking a target.
61. Which instrument is primarily used by forensic ballisticians to measure the pitch of rifling or the rate of twist inside a firearm's barrel?
A. Micrometer
B. Helixometer
C. Taper Gauge
D. Chronograph
Answer: B. Helixometer
Explanation: A helixometer is an optical instrument specifically designed to examine the interior surface of a firearm barrel and measure the pitch of rifling (rate of twist or spiral degree of the lands and grooves).
62. Which instrument is primarily used in forensic ballistics to determine the bore diameter of a firearm?
A. Comparison Microscope
B. Stereoscopic Microscope
C. Taper Gauge
D. Chronograph
Answer: C. Taper Gauge
Explanation: A taper gauge is used to determine the bore diameter of a firearm by measuring the internal diameter of the barrel.
63. Which specialized instrument consists of two microscope optical systems connected by a bridge, allowing a firearm examiner to view two evidence specimens side-by-side in a single field of view?
A. Compound Microscope
B. Comparison Microscope
C. Metallurgical Microscope
D. Onoscope
Answer: B. Comparison Microscope
Explanation: Invented by Dr. Calvin Goddard for forensic applications, the comparison microscope allows side-by-side optical matching of striations on evidence bullets and fired cartridge cases against test-fired samples.
64. Which instrument is used in forensic ballistics to examine the interior surface of a firearm barrel for irregularities, imperfections, scratches, and other conditions?
A. Chronograph
B. Onoscope
C. Helixometer
D. Taper Gauge
Answer: B. Onoscope
Explanation: An onoscope is an instrument used to examine the interior surface of a firearm barrel and detect irregularities, imperfections, scratches, and other conditions within the bore.
65. When determining whether a bullet was fired from a rifled barrel with a right-hand (clockwise) or left-hand (counterclockwise) twist, which feature measured by a helixometer provides this critical class characteristic?
A. Land impression width
B. Groove depth
C. Direction and pitch of rifling twist
D. Primer impression depth
Answer: C. Direction and pitch of rifling twist
Explanation: The helixometer measures the helical angle and direction (twist) of the rifling grooves inside the barrel, establishing fundamental class characteristics of the firearm manufacturer.
66. Which characteristic of rifling can be determined using a helixometer?
A. Width of the land impressions
B. Depth of the grooves
C. Pitch and direction of rifling twist
D. Depth of the primer impression
Answer: C. Pitch and direction of rifling twist
Explanation: A helixometer is used to determine the pitch (rate of twist) and direction of the rifling inside a firearm barrel. These are important class characteristics used in forensic firearm examination.
67. Which type of microscope provides a three-dimensional (3D) view of an object at lower magnification levels, making it ideal for initial preliminary examination of evidence before striation matching?
A. Polarizing Microscope
B. Stereoscopic Microscope
C. Electron Microscope
D. Phase-Contrast Microscope
Answer: B. Stereoscopic Microscope
Explanation: A stereoscopic (or stereo) microscope uses two separate optical paths to create a 3D image, making it ideal for inspecting coarse surface details, tool marks, and general physical evidence before high-power comparison analysis.
68. A firearm examiner uses a taper gauge to assess the degree of constriction at the muzzle end of a shotgun. This constriction feature is known as the:
A. Chamber length
B. Choke
C. Forcing cone
D. Bore pitch
Answer: B. Choke
Explanation: The choke refers to the degree of constriction at the muzzle end of a shotgun barrel designed to control shot pattern spread. A taper gauge is used to gauge internal diameter differences and measure choke size.
69. During internal barrel examination, a forensic examiner uses a light-reflecting mirror attachment inside an onoscope to detect which type of secondary evidence or barrel condition?
A. Muzzle velocity degradation
B. Metal fouling and rust pitting
C. Primer cup composition
D. Anvil indentation depth
Answer: B. Metal fouling and rust pitting
Explanation: Internal barrel inspection devices like the onoscope/borescope use internal lighting and mirrors to allow examiners to detect corrosion, pitting, lead buildup, or manufacturing flaws along the interior bore surface.
70. During the internal examination of a firearm barrel, which of the following conditions can be detected using an onoscope?
A. Muzzle velocity
B. Fouling, rust, pitting, and other bore irregularities
C. Primer composition
D. Depth of the firing-pin impression
Answer: B. Fouling, rust, pitting, and other bore irregularities
Explanation: An onoscope permits examination of the interior of a firearm barrel, allowing the examiner to observe fouling, rust, pitting, scratches, and other irregularities or imperfections within the bore.
71. What term describes the distance advancing along the axis of the barrel required for the rifling to complete one full 360-degree turn, as measured by a helixometer?
A. Caliber
B. Pitch of rifling
C. Depth of groove
D. Land width
Answer: B. Pitch of rifling
Explanation: The pitch of rifling (rate of twist) is defined as the distance along the barrel axis required for a groove to make one complete turn (e.g., 1 turn in 10 inches). The helixometer directly measures this helical parameter.
72. Which component of a comparison microscope allows the examiner to adjust both specimens independently so that matching striation lines can be aligned precisely across the dividing hairline?
A. Objective lenses
B. Optical bridge
C. Mechanical stages/stage movement knobs
D. Eyepiece oculars
Answer: C. Mechanical stages/stage movement knobs
Explanation: The mechanical stages hold the evidence holders and allow x-y-z axis manipulation of both specimens independently, enabling the ballistician to align land and groove striations accurately across the central dividing line.
The mechanical stages hold the specimens and permit controlled movement of each specimen so that corresponding markings can be precisely aligned and compared across the dividing line of the comparison microscope.
Helixometer → pitch of rifling
Taper gauge → bore diameter
Onoscope → internal examination of firearm barrel
Stereoscopic microscope → preliminary examination
Comparison microscope → comparison of fired bullets/cartridge cases
Chronograph → bullet/muzzle velocity
Analytical/torsion balance → weight of bullets/shot/pellets
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