Ballista is latin for "Giant Crossbow" and is the first of many projectiles. Currently, guns have unique identifications based on manufacturer. For instance, Colts produce a left twist groove pattern when all other manufacturers use a right twist groove. Most guns have grooves, with 6 being the most common number. Guns can be analyzed in different ways. This is the residue of unburned particles from the primer and powder combustion.
GSR contains antimony, barium and lead in major quantities. Other possible contents are aluminum, sulfur, tin, calcium, potassium, silicon, and chlorine.
Cartridge casings are also analyzed. The casing may be nickel coated. When a bullet is fired from a gun, the gun leaves microscopic marks on the bullet and cartridge case. These marks are like ballistic fingerprints. The examiner will then assess how similar the two sets of marks are and determine if the bullets are likely to have been fired from the same gun or different guns.
Cartridge cases are compared in the same way. For roughly a century, forensic ballistics experts have been comparing bullets and cartridge cases by visually examining them under a split-screen microscope. After comparing the bullets, the examiner can offer an expert opinion as to whether they match but cannot express the strength of the evidence numerically.
NIST scientists are developing methods that will allow an examiner to attach an objective, statistically meaningful measure of certainty to their testimony. Crime labs use these standards to calibrate their instruments, which helps ensure that their examinations produce accurate results. Used in calibers. The flame is communicated to the powder charge through the vents leading into the powder charge.
So it happens that the engravings on the bullet fired from one barrel will be different from that on a similar bullet fired from another barrel. And conversely, t he engravings on bullets fired from the same barrel will be the same. The imprint on all cartridge cases fired from the same weapon are always the same, those on cartridge cases fired from different weapons must always be different.
They are characteristics whose existence is beyond the control of man and which have a random distribution. Their existence is a firearm is brought about by the tools in their normal operation resulting through wear, tear, abuse, mutilations, corrosion, erosion and other fortuitous causes.
These are the irregularities found on the inner surface of the barrel and on the breech face of the breechblock of the firearm as a result of the failure of the tool beyond the control of the manufacturer to make them smooth as a mirror.
In addition to bullet and cartridge case comparison function examinations and distance determinations; trace evidence such as blood, hair or fiber maybe adhering to exposed surfaces. All of which may yield valuable information to an investigator on his case. Insure the maximum value of this evidence is obtained; it first must be properly identified preserved and packaged. These steps should be documented by good notes and photographs.
NOTE: Photos must contain a scale to show size. Firearms General considerations and precautions: As important as physical evidence or fingerprints may be, safety is of greater concern. Make two marks on the cylinder, one on each side of the top strap, to indicate the chamber that is in the firing position.
If uncocked, these marks will indicate the chamber found indexed in front of the firing pin. Your notes should contain the following information: Appearance of the cylinder as recovered Marks made each side of top strap Diagrams to be used in notes 1 6 2 5 3 4 Direction of rotation Diagrams to be used in notes 1 2 6 3 5 4 Direction of rotation Example Index Card Chamber position Condition 1 2 3 4 5 6 Fired Fired Fired Unfired Loaded Loaded Head stamp U. Cartridge Co.
Remington Arms Co. Winchester Repeating Arms Co. Dominion Cartridge Co. Western Cartridge Co. Peters Cartridge Co. Fired and unfired cartridge should be individually packaged by placing them in soft tissue or cotton, sealed in a pill box or envelope and pertinent information placed on the container. As an alternative to engraving on the weapon, use the serial number for later identification.
You may also affix a tag to the trigger guard. Open the action and visually check the chamber for a cartridge or cartridge case.
If it is possible, lock the slide to the rear keeping the action in the opened position, if not, let the action close then engage any manual safety devices that may be on the weapon. Note: Make sure that no live cartridge is left in the chamber If you mark the weapon for identification, do so somewhere on a part not readily removable from the weapon. The magazine, if found in weapon, may be included in the same item as the weapon for submission to the laboratory, however if it is found not in the weapon, it should be submitted as a separate item.
NOTE: if fingerprinting is requested the cartridges may be left in the magazine but should not be left in the chamber. NOTE: All weapons should be submitted to the property room or crime laboratory unloaded. The firearm should be properly strapped with a nylon tie for safety. If in doubt about proper processing, do not proceed further until contacting the crime laboratory and discussing the situation with a firearms examiner.
Rubber gloves and masks should be worn when DNA is collected or finger printing is needed. Gloves must be changed with each piece of evidence handled. If the weapon must be shipped, it is imperative that it be properly packaged.
It should be placed in a heavy corrugated container and secured in a place to prevent shifting with the container. NOTE: Rifles and shotguns should not be dismantled before packaging as this could alter their evidentiary value. All firearms both handguns and long guns shall be packaged upon submittal to the crime laboratory. Fit packaging for fire arms include: boxes, manila paper envelopes and paper wrapping.
Firearms recovered in water should be submitted in the same water in a watertight container. However, firearms examiner must be contacted prior to submission it is unknown whether the firearm is loaded. They should be packed sealed in a paper envelope or pill box and the container marked for identification. The bullet should not be marked due to the possibility of destroying valuable evidences.
NOTE: Plastic or glass airtight containers should never be used for bullets or firearms. They could allow moisture to cause corrosion of identifiable detail on the bullet and rust on a firearm.
Unless absolutely necessary, do not attempt to dig out projectile. Remove the portion of material in which the projectiles are embedded and submit the entire piece to the crime laboratory. Skip to content. My Account Blog. David Aufiere Columbia, Louisiana Ballistics science has been around since the s. Post Views: 2, Related Posts.
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