Manufacturing of Firearm Barrels

Manufacturing of Firearm Barrels

  • Each barrel has four class characteristics:

    • Caliber (bore diameter): Measured in inches (e.g., .357, .22, .45).

    • Number of lands and grooves: The contours formed inside the barrel that impact bullet stability and accuracy.

    • Direction of twist: The direction in which the lands twist. This can be either right or left.

    • Width of the lands and grooves: The thickness or width of the raised (lands) and recessed (grooves) areas within the barrel.

  • All class characteristics are measurable, which implies precision in forensic analysis.

    • Caliber

    • Number of lands and grooves

    • Width of the lands and grooves

    • Direction of twist

Types of Rifling

  • Polygonal Rifling:

    • Characterized by lands and grooves that have a rounded profile.

    • Produced using Hammer Forging, a process known for enhancing the strength and durability of the barrel.

Class Characteristics - Repetition

  • The core class characteristics previously listed must be emphasized for their importance in forensic analysis:

    • Caliber: The measurement of the internal diameter of the barrel.

    • Number of lands and grooves

    • Width of the lands and grooves

    • Direction of twist

Practice Problem

  • Problem Description:

    • A shooter stands on the 3rd floor of a building, resting the gun on a window ledge 3 feet above the floor.

    • The victim is shot in the stomach, which is also located 3 feet above the ground.

    • The angle of incline from the shooter to the victim is 18 degrees.

    • Objective: Construct a diagram to calculate the distance from the building to the victim.

Caliber and Gauge

  • Caliber:

    • Defined as the internal diameter measurement of the firearm barrel.

    • Measured in either inches or millimeters.

    • For example, a .38 caliber handgun has a barrel diameter of .38 inches.

    • The caliber of recovered bullets can be determined by weighing; larger calibers typically correlate to more power.

    • Common calibers include:

      • .45

      • .40

      • .357

      • .308

      • .270

      • .22

  • Gauge:

    • Defined by the number of lead balls of a specified diameter that equal one pound in total weight.

    • For example, 10 balls of the 10 gauge diameter are equivalent to one pound.

    • Example Gauges:

    • 10 Gauge: 0.775 inches diameter (10 balls make 1 pound)

    • 12 Gauge: 0.725 inches diameter (12 balls make 1 pound)

    • 16 Gauge: 0.665 inches diameter

    • 20 Gauge: 0.615 inches diameter

    • 28 Gauge: 0.5457 inches diameter

    • .410 Bore: 0.410 inches diameter

    • Each gauge corresponds to a specific barrel diameter; smaller gauge sizes typically denote more power.

Striations

  • Striations:

    • These are the unique marks on the bullets, resulting from the rifling patterns present in the gun barrel.

    • They provide forensic evidence linking a bullet back to the specific firearm it was fired from, allowing for analysis and identification.