Chapter 16
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Action Alternative light sources (als): Light sources that employ light of different wavelengths (colors) to visualize the components of an impression. Barrel: The metal pipe that guides the initial flight of the bullet. Breech: The end of the gun barrel nearest to the action. Breech block (or face): The back of the firing chamber. Breech-loading Firearm: A weapon in which the ammunition and bullet are placed directly into the firing chamber without having it put down the barrel. Broach cutter: A tool used to simultaneously cut all of the rifling grooves by forcing the cutter head down a smooth, drilled-out gun barrel while rotating the cutter with a characteristic twist rate. Button Rifling: A process in which a small, shaped form is forced down the smooth gun barrel at very high pressures, compressing rather than cutting the metal into the grooves to form a rifled barrel. Cartridge: Ammunition made up of casing, primer, powder, wadding and bullet. Casting: A physical replica of an impression, formed by a moldable material, that sets into an actualsized, permanent reproduction of the original impression. Chamber: The enclosure in a gun’s design that contains the cartridge when ready to fire. Dental stone: A gypsum product that when mixed with water and pored into a mold sets to form a hard, strong and stable solid that doesn’t require reinforcement.
The mechanical apparatus of a firearm that loads, fires and ejects the cartridge.
Drag
The force that opposes the forward motion of the bullet created by air resistance.
External (intermediate) ballistics
The study of the flight of the bullet from the time it leaves the end of the gun barrel until it reaches the target.
Ballistics
The study of how projectiles move through space.
Caliber
The diameter of the gun barrel in 1/100th of a inch.
Air gun
Weapons that move a projectile solely by the release of stored gas pressure rather than through combustion.
Fixed ammunition Flintlock weapon: Firearms that use a spark created by moving a piece of flint over a steel plate (“frizzen”) to ignite a small primer charge that then sets fire to the main charge. Firearm: An assembly consisting of a barrel and a mechanical action that allows a projectile(s) to be propelled forward through the action of an extremely fast combustion reaction. Firearms identification: The process of determining “if a bullet, cartridge case or other ammunition component was fired by a particular firearm.”
Ammunition that combines primer, an accurately measured main charge and the bullet all enclosed in a single, easily handled, water-tight casing.
Gunshot residues
Deposits of unreacted explosive materials and solid combustion byproducts that are discharged from openings in the gun into the nearby environment upon firing.
Shotgun
A type of long gun without rifling that uses ammunition containing either many small pellets (shot) packed into a single cartridge or a single, solid projectile (slug).
Visible impressions
Impression evidence that is readily observable without any visualization aids
Terminal Ballistics
The study of what happens when a projectile hits its target.
Types of Ballistics
Internal, external, and terminal
Types of Ballistics
Internal, external, and terminal
Handgun
Smaller firearms that are designed for operation using one hand.
Serial number restoration
The process of making visible serial numbers stamped into a gun that have been filed or ground away.
Primer
The shock sensitive compound that ignites the main charge of a cartridge upon being struck.
Revolver
A firearm in which ammunition is moved into place for firing by means of rotating a cylinder that contains a number of separate firing chambers loaded with filled cartridges.
Positive image
An image created when an object leaves something behind on the surface which can be visualized.
Rifling
Spiral grooves inside of the gun’s barrel which cause the projectile to spin about its long-axis.
Round
An intact unit ammunition (primer, bullet or “slug” and main charge).
Plastic impressions
Impression evidence that have been formed when an object is imprinted into a soft, moldable material.
Gravity
The force that constantly pulls objects downward with a constant force, defined as F = mg (where m is mass and g is the gravitational constant).
Grooves
The places where some of a gun’s barrel metal has been removed (rifling) or shaped to create a depression.
Grooves
The places where some of a gun’s barrel metal has been removed (rifling) or shaped to create a depression. (Makes gimps on the bullet, raised parts)