Cartridge and Firearm Anatomy
The complete, unfired unit of ammunition consisting of a casing, primer, gunpowder, and projectile.
What is a cartridge (or round)?
The raised helical ridges left inside a gun barrel during manufacturing that bite into the bullet to impart stabilizing spin.
What are lands?
The curved parabolic path that a bullet follows through the air after leaving the barrel until it hits a target.
What is trajectory?
The permanent physical path or tunnel created through tissue as a bullet penetrates the body.
What is a permanent cavity?
Unburned propellant particles, metallic traces, and chemical soot blown out of a firearm during discharge.
What is Gunshot Residue (GSR)?
The projectile that is expelled from the firearm barrel when a cartridge is discharged.
What is a bullet?
The spiral cut-out channels in a rifled barrel located between the raised lands.
What are grooves?
The aerodynamic friction and air resistance that acts opposite to the motion of a bullet during flight.
What is drag?
A reddish-brown ring surrounding an entry wound caused by friction from the bullet scraping skin upon entry.
What is an abrasion ring?
Small pinpoint burns or unburned powder specks embedded in skin around an entry wound, indicating an intermediate shooting distance.
What is stippling (or tattooing)?
The shock-sensitive chemical cup at the base of a cartridge casing that ignites the main gunpowder charge when struck by the firing pin.
What is the primer?
Microscopic, parallel scratches left on a bullet as it slides along the lands and grooves of a barrel, providing individualizing evidence.
What are striations?
The unstable, fish-tailing wobble of a bullet in flight pivoting around its center of gravity.
What is yaw?
The rapid stretching and expanding of tissue surrounding a bullet path caused by high-energy hydraulic shockwaves.
What is a temporary cavity?
The national automated database maintained by the ATF that allows crime labs to compare 3D images of spent cartridges and bullets across jurisdictions.
What is NIBIN (National Integrated Ballistic Information Network)?
Firearm design characterized by smooth inner barrel walls lacking spiral lands and grooves, typically found in shotguns.
What is a smoothbore?
The internal diameter of a rifled firearm barrel, usually expressed in hundredths of an inch or millimeters.
What is caliber?
The trigonometric function used to calculate impact angle ($\theta$) by dividing the minor axis of an entry hole by its major axis
What is inverse sine (or arcsine)?
The characteristic cone-shaped flaking or chipping pattern seen on the exit side of impacted bone or glass.
What is beveling?
Mechanical impressions left on the base of a shell casing when high pressure forces it backward against the rear wall of the firing chamber.
What are breechblock markings (or breechface impressions)?
Stamped lettering or numbers on the base of a cartridge casing that identifies the manufacturer, caliber, or year of production.
What is a headstamp?
A dual-view optical instrument that allows a forensic scientist to observe two bullets or shell casings side-by-side to match striation patterns.
What is a comparison microscope?
The estimated 3D spatial location from which a shot was fired, determined by extending trajectory lines backward through impact barriers.
What is the point of origin?
A star-shaped entry wound produced when a firearm muzzle is pressed directly against skin over bone, causing expanding propellant gases to tear tissue outward.
What is a stellate (or contact) wound?
A chemical spot test that turns dark pink or purple in the presence of nitrites from burned gunpowder residue.
What is the Modified Griess Test?