A shell moments after leaving the barrel of a gun.
Forensic Ballistics

The word "ballistics" comes from the greek word βάλλειν, meaning "throw". In its truest sense, ballistics is the study of the mechanics of flight of a projectile.
Forensic ballistics is the science of analyzing firearm usage in crimes. Specifically, the analysis of bullets, firearm and tool mark examinations (Ballistic fingerprinting), and the interaction of a projectile with its target (Terminal ballistics). It also involves trajectory physics (for crime scene reconstruction), and can even branch as far as matching and identification of wound patterns caused by different firearms and ammunition. From this, scientists can determine whether a certain firearm or tool was used in the commission of a crime.
Contrary to popular belief, however, forensic scientists cannot determine conclusively if a suspect has discharged a firearm. Recent tests have shown that previously accepted Gunshot residue (GSR) evidence is not as solid as once thought, as particles will stay in the air up eight minutes after the firearm's discharge.

Warlow, Tom A., Firearms, The Law, and Forensic Ballistics (2nd Ed.), CRC Press LLC, Florida, 2004 "What is Forensic Ballistics", (27/09/2009)
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