Test Firing

Test firing

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In any case where a firearm has been used, there are many clues that are left behind. An investigator might find a piece of the bullet (fragment), a casing, the whole weapon, bullet holes or GSR (Gunshot Residue). All of these clues can be used to match a suspect weapon with the scene of a crime.
In any case where a firearm has been used, there are many clues that are left behind. An investigator might find a piece of the bullet (fragment), a casing, the whole weapon, bullet holes or GSR (Gunshot Residue). All of these clues can be used to match a suspect weapon with the scene of a crime.

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Bullet fragments may contain markings that were imprinted by passing through the barrel. Even though each barrel may be made the same way, differences in the metal (and wear) will result in unique patterns on a bullet that passes through the barrel.

Each barrel has different lands and grooves. The "lands" are the raised parts inside the barrel, and the "grooves" are the recessed portion. The number of lands and grooves, their size and shape, may assist in determining the make and the type of weapon that was used.

When each barrel is produced, there are differences that are unnoticeable to the human eye which may only appear under a microscope. The marks left on the projectile (bullet) are from the lands and grooves as well as finer scratches that have resulted from use or production.

No two barrels will give the exact same markings on a bullet (like a fingerprint). The Firearms Specialist may take the weapon in question and fire it into water and retrieve the test bullet. The test bullet is then compared to the fragment using a comparison microscope. If it is a match, a photograph may be taken for use as evidence in court.
Bullet fragments may contain markings that were imprinted by passing through the barrel. Even though each barrel may be made the same way, differences in the metal (and wear) will result in unique patterns on a bullet that passes through the barrel.

Each barrel has different lands and grooves. The "lands" are the raised parts inside the barrel, and the "grooves" are the recessed portion. The number of lands and grooves, their size and shape, may assist in determining the make and the type of weapon that was used.

When each barrel is produced, there are differences that are unnoticeable to the human eye which may only appear under a microscope. The marks left on the projectile (bullet) are from the lands and grooves as well as finer scratches that have resulted from use or production.

No two barrels will give the exact same markings on a bullet (like a fingerprint). The Firearms Specialist may take the weapon in question and fire it into water and retrieve the test bullet. The test bullet is then compared to the fragment using a comparison microscope. If it is a match, a photograph may be taken for use as evidence in court.

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Barrel Cross Section

Barrel cross section

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Lands & Grooves

Lands & grooves

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Weapon Barrels In Production

Weapon barrels in production

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Bullet Fragment

Bullet fragment

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Casings contain information about the type of ammunition, stamped onto the base of the cartridge. But there is more information hidden on the casing. Parts of the firearm which come in contact with the casing may leave markings. Just like the marks left behind from the lands and grooves, these are unique and can be compared to the suspect weapon.
Casings contain information about the type of ammunition, stamped onto the base of the cartridge. But there is more information hidden on the casing. Parts of the firearm which come in contact with the casing may leave markings. Just like the marks left behind from the lands and grooves, these are unique and can be compared to the suspect weapon.

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Bullet in Flight

Bullet in flight

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Gunshot residue (GSR) is a fine powdery substance that results from the discharge of a cartridge. When a weapon is fired this residue spreads all over, and can be found using methods at the forensic laboratories. These tiny particles settle like dust over the victim, shooter and environment. Some of the particles are blasted into the target area as well. GSR includes particles from the primer, the casing itself and from the bullet in addition to "the combustion of the gun powder."

The GSR can be found on clothing, furniture and even on the suspect! The suspect will have adhesive lifts applied to his or her hands and these will be sent to the lab. At the laboratory, the lifts will be checked for GSR. The chemistry section use a S.E.M. (Scanning Electron Microscope) to see the particles which are very small. You can see the GSR on the tip of a pin!

These small particles may be caught in the suspect’s hair or clothes or may even be brushed off onto other objects (like a car seat).
Gunshot residue (GSR) is a fine powdery substance that results from the discharge of a cartridge. When a weapon is fired this residue spreads all over, and can be found using methods at the forensic laboratories. These tiny particles settle like dust over the victim, shooter and environment. Some of the particles are blasted into the target area as well. GSR includes particles from the primer, the casing itself and from the bullet in addition to "the combustion of the gun powder."

The GSR can be found on clothing, furniture and even on the suspect! The suspect will have adhesive lifts applied to his or her hands and these will be sent to the lab. At the laboratory, the lifts will be checked for GSR. The chemistry section use a S.E.M. (Scanning Electron Microscope) to see the particles which are very small. You can see the GSR on the tip of a pin!

These small particles may be caught in the suspect’s hair or clothes or may even be brushed off onto other objects (like a car seat).

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Gun Powder Residue

Gun powder residue

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Learning Objectives

The learner will:
  • Develop enthusiasm and continuing interest in the study of science
  • Describe examples of the application of technology in society

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