 Rifling-impressing of the inner surface of a gun barrel with spiral grooves. › Imparts spin to projectile to keep it on course › No two barrels have identical striation markings. › The striations leave their markings on a bullet.

 The class characteristics of a rifled barrel include the number of lands and grooves and the width and direction of twist.

 The comparison microscope allows for two bullets to be looked at simultaneously.

 The firing pin, breechblock, and ejector and extractor mechanism also offer a highly distinctive signature for individualization of cartridge cases.  Shot guns are not rifled. The barrel is smooth and therefore is useless in comparison of two shotgun shells.

 Storage of bullet and cartridge surface characteristics is similar to the storage of automated fingerprint files.  Two automated firearms search systems: › DRUGFIRE developed by FBI › IBIS developed by ATF  NIBIN is a search system that incorporates both DRUGFIRE and IBIS

 Distance from which a gun was fired is determined using gunpowder particles and discharge residues found around a bullet hole.  Residue patterns on the victims clothing are compared to test patterns (made by the suspect gun)to determine precise distance from where a gun was fired.  Greiss test-chemical test used to develop patterns around a bullet hole.

 Firing a weapon: › Propels residue toward the target › Blows gunpowder and primer residue toward the shooter.  Traces of these often land on the hand of the shooter.  Amount of barium and antimony is measured on the suspects hand. › Shows whether a person has fired a gun or was standing near a gun fired.

 Serial #s that were obliterated or removed can be restored.  Restoration can occur through chemical etching. (Due to metal crystals extending short distance under original #s).  Picking up a firearm by inserting an object into the barrel can alter the striation markings on test-fired bullets.  A weapons hammer and safety position should be recorded before the weapon is unloaded. This include the location of all fired and unfired ammunition.  Protection of markings on bullet and cartridge casings is a primary concern.

 Minute imperfections in tools signify individuality.  The shape and patterns of imperfections are further modified by damage and wear during the tools lifetime.  Comparison microscopes are used to compare crime-scene tool marks w/ test impressions made with a suspect tool

 Shoe and tire marks found at crime scenes are best preserved by photography and casting.  Barley visible dust prints are recovered using the electrostatic lifting technique  Bloody footwear impressions are visualized by chemical enhancement.