Forensics Ballistics quiz

List the class characteristics of a rifled barrel.

# of lands and grooves, caliber, and direction of twist.

Why should a suspect firearm never be picked by inserting an object into its barrel?

A suspect firearm should never be picked up by inserting an object into its barrel because this practice disturbs powder deposits, rust, or dirt lodged in the barrel, and consequently may alter the striation markings on test-fired bullets.

How should a suspect weapon discovered underwater be transported to the laboratory and why?

A weapon recovered from underwater should be transported to the laboratory in a receptacle containing enough of the same water in which it was found.

As the distance to the target of a shotgun blast increases, what do the pellets do?

As the distance to the target of a shotgun blast increases, the pellets separate and spread out.

What is bullet wipe? Of what does it consist?

Bullet wipe is a dark ring formed around the perimeter of an entrance hole that is wiped off the bullet's surface as it passes through the target. Bullet wipe consists of a mixture of carbon, dirt, lubricant, primer residue, and lead.

What is caliber?

Caliber is the measure of the diameter of the bore of a rifled firearm.

What is distance determination and upon what is it based?

Distance determination is the process of determining the distance between the firearms and a target. It is usually based on the distribution of powder patterns or the spread of a shot pattern.

True or False: As a shotgun shell passes through a barrel, its surface is impressed with striations from the lands and grooves of the barrel

False

True or False: Barium and antimony specimens found in primer on a suspect's hand after firing a gun remain for a period of 36 hours and confirm the suspect's involvement in a crime approximately 75 percent of the time.

False

True or False: Rifled barrels manufactured in succession will have identical striations markings

False

True or False: Unlike other areas of criminalistics, the goal of individualization is not yet reality in firearm and tool mark examination

False

What are grooves and lands?

Grooves are the cut or low-lying portions between the lands in a rifled bore. Lands are the raised portion between the grooves in a rifled bore.

What is NIBIN?

NIBIN is the National Integrated Ballistics Information Network.

How are striations used for comparing bullets?

No two rifled barrels have identical striations. As the bullet passes through the barrel, its surface is impressed with striation from the lands and grooves of the barrel. A firearms examiner can compare the striation on a bullet recovered at a crime scene to those made on bullets test fired from a suspect gun. If the markings match, this indicates that the recovered bullet was fired by the suspect weapon.

Briefly describe the sequence of events that occurs from the time the trigger of a firearm is pulled to the time the bullet is fired.

Pulling a trigger releases the weapon's firing pin, causing it to strike the primer, which in turn ignites the powder. The expanding gases generated by the burning gunpowder propel the bullet forward through the barrel.

The raised areas between the grooves in a rifled bore are called

Rifling

What is rifling and what is its purpose?

Rifling refers to the spiral grooves impressed in the bore of a firearm barrel. Rifling imparts spin to the projectile when it is fired, which keeps it on an accurate course.

What are striations? How are they produced?

Striation are markings impressed into the metal of a barrel. They are produced as the minute imperfections found on the rifling cutter's surface, or by minute chips of steel pushed against the barrel's inner surface by a moving broach cutter.

What is the Griess Test? What substance is being tested for in this procedure?

The Greiss test is a chemical test used to develop patterns of gunpowder residue around the bullet holes. It tests for the presence of nitrates.

What parts of a firearm leave impressions on a cartridge case that constitutes individual characteristics of that weapon?

The parts of a firearm that leave impressions on the cartridge case that constitute individual characteristics of that weapon are the firing pin, the breechblock, the ejector, and the extractor.

Briefly describe how a firearms examiner makes a distance determination for a handgun or rifle shot.

The precise distance from which a handgun or rifle was fired is determined by carefully comparing the powder residue pattern on the victim's clothing or skin to test patterns made by firing the suspect weapon at varying distances from a target. By comparing the test evidence patterns, the examiner may find enough similarity in shape and density on which to judge the distance from which the shot was fired.

Name three factors that can prevent a firearm examiner from obtaining a perfect match of striation markings around the periphery of two bullets.

Three factors that can prevent a firearms examiner from obtaining a perfect match of striation markings around the periphery of two bullets are (1) The presence of grit and rust can alter the markings on bullets fired through the same barrel; (2) bullets may become so mutilated and distorted on impact as to yield only a small area with intact markings; and (3) striator markings on a barrel are not permanent structures; they are subject to continuing alteration through wear as succeeding bullets traverse the length of the barrel.

How does a shotgun barrel differ from the barrel of a handgun? How does this difference affect the ability of a firearms examiner to compare shotgun shells?

Unlike handguns, a shotgun is not rifled-- it has a smooth barrel. Because of this, shotgun shells are not impressed with any characteristic markings that can be used to compare two shotgun shells to determine if they were fired from the same weapon.

How does a firearms examiner estimate a distance determination for a shooting involving a shotgun?

With a shooting involving a shotgun, a distance determination can be estimated by measuring the spread of the discharged shot.

The most important tool available to the firearms examiner in the identification of firearms is

the digitizing videocamera