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Ballistic Evidence
| Term | Definition |
|---|---|
| headstamp | the bottom of a cartridge that includes information on the cartridge manufacturer and caliber |
| primer powder | when the firing pin strikes the headstamp, a spark lights this substance which start the chemical reaction that fires the bullet |
| gunpowder | this substance fills most of the cartridge casing and undergoes combustion to fire the bullet out of the gun barrel |
| casing | the is usually made of brass, aluminum, nickel, or steel and is wrapped around all of the components of a cartridge; it is often discarded from the gun when the gun is fired |
| cartridge | this is the name for the combination of the casing, bullet, gunpowder, and primer powder. |
| bullet | this is the cartridge component that is fired from the gun barrel; the barrel leaves markings on it as it moves through the barrel |
| rifling | this is the name of the cuts in the gun barrel that help guide the bullet down the barrel; it is also the name for the cuts left in the bullet as a result of the barrel cutting it |
| twist | this describes direction of the rifling "lean" on a bullet; it can be "left" or "right" |
| gunshot residue (GSR) | this is the mix of gases and powders that are released from the gun upon firing; it can be found on people/objects that were close to the gun when it was fired |
| entrance wound | this results from a bullet being shot into a person; it is the smaller of the two wounds usually created, due to the material being pushed inward by the bullet |
| exit wound | this results from a bullet being shot into a person; it is the larger of the two wounds usually created, due to the material being pushed outward by the bullet |
| ballistic gel | this is used to observe how a bullet moves through the human body; similar to the human body, it expands when the bullet moves through it but then snaps back to its original shape |
| ballistic soap | this is used to observe how a bullet moves through the human body; it can be used to observe yaw damage because it retains all damage done to it and doesn't reform itself after the bullet has passed through |
| long guns | these types of firearms require two hands effectively shoot them |
| hand guns | these types of firearms are small enough to be operated with one hand |
| semi-automatic | in these types of firearms, the gun automatically readies the bullet to be fired, but a trigger must be pulled to fire it |
| fully automatic | in these types of firearms, the trigger can be held down, and the gun automatically readies each new bullet and keeps firing |
| repeating | in these types of firearms, a step must be taken after firing to ready a new bullet; examples include pump-action, lever-action, and bolt-action |
| lands | these are the elevations created by the gun barrel leaving markings on the bullet; they tend to be the wider of the two types of markings on the bullet |
| grooves | these are the indentations created by the gun barrel leaving markings on the bullet; they tend to be the narrower of the two types of markings on the bullet |
| sequence of events in firing a bullet | trigger is pulled, hammer is moved & the tip of the hammer (the firing pin) slams into the bullet headstamp; the primer powder is ignited, which then ignites the gunpowder; the pressure of the gases from the explosion pushes the bullet out of the barrel |
| caliber | this describes the diameter of a bullet (the width of a bullet) |
| yaw damage | this is caused by a bullet spinning/twisting as it travels through a substance |
| firing pin marks | these are left by the tip of the hammer slamming into the headstamp of the cartridge; it is usually found near the middle of the headstamp (centerfire), but it can be found near the edge (rimfire); they are individual evidence |
| extractor/ejector marks | these are created when a cartridge casing is discarded from a gun and receives scrapes, cuts, or gouges at the headstamp; they are individual evidence |
| breechblock face markings | these are created due the headstamp undergoing pressure while the gun is fired; types include parallel, arched, granular, and circular; they are individual evidence |
| bullet trajectory | this is another term for the path of a bullet; if a gun is fired while pointing straight ahead, this is an arc downward until the bullet hits an obstacle or the ground |
| polygonal rifling | this kind of rifling results from the barrel not cutting the bullet but instead squeezing it, creating smooth transitions between the lands and the grooves |
| bullet wipe | because a bullet can get a dark-colored "soot" on it from moving through the gun barrel, this can happen when the bullet enters its first object, leaving a dark smudge at the bullet entrance |
| hollow point bullet | this kind of ammunition expands when it enters a substance, causing much more internal damage and usually stopping quicker within the substance because of this, instead of exiting the substance |
| full metal jacket | this type of ammunition is totally covered in an outer shell of harder metal, covering a lead interior |
| nitrate test for GSR | this test is done using diphenylamine; not used as much anymore because many products contain the substance tested for, so it can cause false positives |
| SEM test for GSR | this tests for the presence of lead, barium, and antimony as an indicator of GSR; this is the most accurate test used today |
| cut rifling | this kind of rifling results from the barrel cutting into the bullet , creating distinct transitions between the lands and the grooves |
| revolver | this firearm, which has a rotating cylinder to hold the ammo, is especially likely to result in a lot of GSR deposited on the shooter's hand due to the more open design of the chamber |
| ballistic class evidence | examples of this include bullet weight, number of lands, width of lands & grooves, rifling twist, and caliber |
| bullet angle of impact | the angle at which the bullet contacts a surface; calculated by calculating the inverse sin of the bullet hole width divided by bullet hole height |
| shotgun | this firearm shoots many small projectiles instead of a bullet through an unrifled barrel |
| pistol | this firearm is a type of handgun that often has cartridges loaded into the grip of the weapon |
| comparison microscope | this device allows the user to look at multiple bullet specimens at once in order to see how similar they are and check for a match |
Created by:
Tdavenport
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