more at http://quickfound.net/
Federal Bureau of Investigation training film: "Shows techniques and methods used by FBI firearms investigation unit in identifying, comparing, and examining bullets, cartridges, firearms, residue, fingerprints, and other evidence for possible identification of weapons used in crimes..."
Public domain film from the National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and equalization.
Small Arms playlist: http://www.youtube.com/playlist?list=PL22A5611941174745
http://en.wikipedia.org/wiki/Ballistic_fingerprinting
Ballistic fingerprinting refers to a set of forensic techniques that rely on marks that firearms leave on bullets to match a bullet to the gun it was fired with...
History
Rifling, which first made an appearance in the 15th century, is the process of making grooves in gun barrels that imparts a spin to the projectile for increased accuracy and range. Bullets fired from rifled weapons acquire a distinct signature of grooves, scratches, and indentations which are of value for matching a fired projectile to a firearm.
The first firearms evidence identification can be traced back to England in 1835 when the unique markings on a bullet taken from a victim were matched with a bullet mold belonging to the suspect. When confronted with the damning evidence, the suspect confessed to the crime. Alexandre Lacassagne was the first scientist to try to match an individual bullet to a gun barrel.
The first court case involving firearms evidence took place in 1902 when a specific gun was proven to be the murder weapon. The expert in the case, Oliver Wendell Holmes, had read about firearm identification, and had a gunsmith test-fire the alleged murder weapon into a wad of cotton wool. A magnifying glass was used to match the bullet from the victim with the test bullet.
Calvin Goddard, physician and ex-army officer, acquired data from all known gun manufacturers in order to develop a comprehensive database. With his partner, Charles Waite, he catalogued the results of test-firings from every type of handgun made by 12 manufacturers. Waite also invented the comparison microscope. With this instrument, two bullets could be laid adjacent to one another for comparative examination.
In 1925 Goddard wrote an article for the Army Ordnance titled "Forensic Ballistics" in which he described the use of the comparison microscope regarding firearms investigations. He is generally credited with the conception of the term "forensic ballistics," though he later admitted it to be an inadequate name for the science.
In 1929 the St. Valentine's Day Massacre led to the opening of the first independent scientific crime detection laboratory in the United States.
Techniques
Ballistic fingerprinting techniques are based on the principle that all firearms have inevitable variations due to marks left by the machining process, leaving shallow impressions in the metal which are rarely completely polished out. Also, normal wear and tear from use can cause each firearm to acquire distinct characteristics over time.
Gross differences
The simplest considerations are the gross differences. A 10 mm bullet, for example, could not have been fired from a 9 mm barrel.
Striations
When a bullet is fired through a rifled barrel, the raised and lowered spirals of the rifling etch fine grooves called "striations" into the bullet. These can be matched with the barrel through which the bullet was fired. Examiners distinguish between striations common to all guns of a particular type ("class characteristics") and those unique to a particular gun ("individual characteristics").
The class characteristics depend upon the type of rifling in the barrel, which varies among manufacturers and models in number and shape of the grooves, twist rate, and direction. Colt, for example, traditionally uses a left-hand twist, while Smith and Wesson uses a right hand twist; a current production M16 rifle uses a 1 in 7 inch twist, while most civilian AR-15s and the current Mini-14 use a 1 in 9 inch twist. Marlin Firearms use a distinctive 16-groove Micro-Groove rifling in many of their firearms, while the M1903 Springfield rifle had two, four, or six grooves depending on the manufacturer. Polygonal rifling may leave striations that are difficult to match to a particular barrel.
Individual characteristics are caused by imperfections in the rifling process and tools, but also by the wear and tear caused by regular use, and can therefore change over time. Criminals or those concerned with government intrusion in privacy sometimes attempt to alter a gun's individual characteristics by changing or shortening the barrel, or by rubbing its interior with a steel brush...
Loading...
13:00
M14 Rifle: "U.S. Rifle 7.62mm M14 Operation and Cycle of Function" pt2-2 1960 US Armyby webdev171,248 views
Link to this comment:
All Comments (0)