Unit 2 Chapter 9a

What are two features of a Semi-automatic pistol?

-Feature a removable magazine -Fire one shot per trigger pull

How does a semi-automatic fire?

A semiautomatic long gun uses the energy from the firing reaction to expel the spent cartridge case, load the next round, and cock the hammer.

What is the choke of a shotgun?

A shotgun barrel can also be narrowed toward the muzzle. This narrowing of the barrel is called the choke of the shotgun.

How are Lands and Grooves made?

By the process called rifling

How is rifling accomplished?

Cutting all grooves in one pass with a cutter known as a broach, or Pressing all the grooves at once onto the barrel with a tool known as a button, or Hammer-forging the barrel over a mandrel containing the reverse image of the rifling.The gun barrel is produced from a solid bar of steel that has been hollowed out by drilling.

Lands and grooves are individual characteristics (True or False)

False?

Is individualization possible with firearms?

Individualization, a goal of in all areas of criminalistics, frequently becomes an attainable reality in firearm and tool mark examination.

What is NIBIN and what does it stand for?

National Integrated Ballistic Information Network and it is a database that is contains images of ballistic evidence, both projectiles and casings, obtained from crime scenes and recovered firearms that can be searched.

Which type(s) of firearms have lands and grooves?

Rifles and handguns

What are lands and grooves?

The ridges (lands) and depressions (grooves) found on the inside of a firearm's barrel that are created when the firearm is manufactured

In rifling, which part of the barrel is not cut? The lands or grooves?

The surfaces of the original bore remaining between the grooves are called lands. · THINK: Lands are not changed, and grooves are made.

What is the purpose of lands and grooves in a rifle?

These lands and grooves force the bullet to rotate as it travels along it. They increase the accuracy of a rifle.

How can the firing pin, breech, lands and grooves and striations be paramount to individualization?

They each leave highly distinctive marks on the bullet or cartridge that are specific to the gun.

What do shotguns fire?

small round pellets called shots or single projectiles called slugs

In addition to a tear pattern, what else will you see when the victim has a contact or less than 1 inch from the target wound?

· A rim of a smokeless deposit of vaporous lead

Who invented the comparison microscope?

· Calvin Goddard

What happens when a weapon is discharge more than 3 feet from the wound?

· It will usually not deposit any powder residues, and the only visual indication is a dark ring around the hole, known as a bullet wipe.

What part of the barrel causes the class and characteristics of the weapon?

· Lands and grooves

Why/How can you determine that a bullet was fired from a particular gun?

· No two rifled barrels will have identical striation markings. · The number of lands and grooves and their direction of twist are obvious points of comparison during the initial stages of an examination between an evidence bullet and a test-fired bullet. Helps you identify what type of gun it was fired from. · Any differences in these class characteristics immediately serve to eliminate the possibility that both bullets traveled through the same barrel. · Individualization, a goal of in all areas of criminalistics, frequently becomes an attainable reality in firearm examination.

Which firearm(s) do not have lands and grooves.

· Shotguns

What part of the barrel gives you the class characteristics of a firearm?

· Striations

How can an investigator determine if a shooter recently fired a weapon?

· The firing of a weapon not only propels residues toward the target, but gunpowder and primer residues are also blown back toward the shooter. · As a result, traces of these residues are often deposited on the firing hand of the shooter, and their detection can provide valuable information as to whether or not an individual has recently fired a weapon. · Examiners measure the amount of barium and antimony on the relevant portion of the suspect's hands, such as the thumb web, the back of the hand, and the palm. · They may also characterize the morphology of particles containing these elements to determine whether or not a person has fired, handled a weapon, or was near a discharged firearm.

What should never be done when looking at/comparing tool marks?

· Under no circumstances must the crime scene investigator attempt to fit the suspect tool into the tool mark. · Any contact between the tool and the marked surface may alter the mark and will, at the least, raise serious questions about the integrity of the evidence.

What are points of comparisons?

· When comparing two objects, you are looking for a sufficient number of points of comparison or the uniqueness of such points to support a finding that both the questioned and test impressions originated from one and only one source. · New computer software and web sites may be able to assist in making shoe print and tire impression comparisons. · Also, bite mark impressions on skin and foodstuffs have proven to be important evidence in a number of homicide and rape cases.

Which distribution pattern of gunpowder particles and other discharge residues around a bullet hole will be present when a rifle or handgun was fired 12 to 18 inches or less?

· halo of vaporous lead (smoke) deposited around a bullet hole. This image is 6 inches.

Which distribution pattern of gunpowder particles and other discharge residues around a bullet hole will be present when a rifle or handgun was fired up to 25 inches (and occasionally as far as 36 inches)?

· scattered specks of unburned and partially burned powder grains without any accompanying soot

Lands and Grooves are class characteristics.

1. Once a manufacturer chooses a rifling process, the class characteristics of the weapon's barrel will remain consistent; each will have the same number of lands and grooves, with the same approximate width and direction of twist. Class characteristics can help identify the type of weapon a bullet was fired from. It cannot tell you which individual gun it was shot from.

What happens when a trigger is pulled on a gun?

1. The trigger serves to release the weapon's firing pin 2. The firing pin strikes the primer (in the cartridge) which in turn ignites the gun powder 3. The expanding gases generated by the burning gunpowder propel the bullet forward through the barrel, simultaneously pushing the spent cartridge case or shell back with equal force against the breech face. 4. The shell is impressed with markings by its contact with the metal surfaces of the weapon's firing and loading mechanisms.

What is the purpose of the choke of a shotgun?

A shotgun barrel is narrowed toward the muzzle (choke) in order to concentrate shot when fired.

How many barrels does a shotgun have and how are they arranged?

A shotgun may be single or double barreled. The two barrels of a double-barreled shotgun may be arranged horizontally (side by side) or vertically (one over another).

How do lands and grooves work?

As a fired bullet travels through a barrel, it engages the rifling grooves; these grooves then guide the bullet through the barrel, giving it a rapid spin. This is done because a spinning bullet does not tumble end over end on leaving the barrel, but remains instead on a true and accurate course. THINK: Lands are not changed, and grooves are made.

What does the movement of a bolt mechanism do in a bolt-action long gun?

Expels the spent cartridge case, loads the next round, and cocks the hammer.

Computer imaging has come very far. With the advent of the NIBIN database and computer comparison, whatever the computer determines is always correct and is what is used in court. True or False?

FALSE· It is important to remember, however, that the ultimate decision for making a final comparison will be determined by the forensic examiner through traditional microscopic methods.

What is the purpose of lands and grooves?

IT ALLOWS FOR A MORE ACCURATE SHOT. As a fired bullet travels through a barrel, it engages the rifling grooves; these grooves then guide the bullet through the barrel, giving it a rapid spin. This is done because a spinning bullet does not tumble end over end on leaving the barrel, but remains instead on a true and accurate course. THINK: Lands are not changed, and grooves are made.

What is individualization in forensics?

In forensic science, individualization refers to the discrimination of an individual from a group through examining unique characteristics of a piece of evidence. Individualization will be successful when these characteristics can be attributed to a common source with an extremely high degree of certainty. In other words you can tell the blood sample is from an individual (particular) person, a bullet was shot by an individual (particular) gun, etc.

Which distribution pattern of gunpowder particles and other discharge residues around a bullet hole will be present when a rifle or handgun was fired over three feet from its victim?

It will usually not deposit any powder residues, and the only visual indication is a dark ring around the hole, known as a bullet wipe.

So then how or why can you match a bullet (inidividualize) to a particular gun?

No two rifled barrels, even those manufactured in succession, have identical striation markings. These striations form the individual characteristics of the barrel.

What are the parts of the bullet? Or cartridge?

Notice from the picture of the cartridge how the bullet is separate from the cartridge. The bullet is propelled forward and the shell is pushed back against the breechface. It is eventually ejected from the gun.

What is rifling and what is its purpose?

Rifling is the process of hallowing out the steel barrel. The purpose is to increase accuracy.

What markings are left on the shot from shotguns?

Shotguns generally fire small lead balls or pellets that are not impressed with any characteristic markings that can be related back to the weapon.

What kind of shot mechanism do long guns have?

Single-shot, repeating, semi-automatic, or automatic.

How are the barrel of a rifle and the barrel of a shotgun different?

The barrel of a shotgun is smooth, without the grooves and lands found in rifles.

If a shotgun has two barrels, do they have the same choke?

The barrels can have different choke diameters.

Where does the breech face leave a mark that is paramount to individualization?

The cartridge case, in its rearward thrust, is impressed with the surface markings of the breechface.

What are the steps in handling impressions?

· Before any impression is moved or otherwise handled, it must be photographed (including a scale) to show all the observable details of the impression. · If the impression is on a readily recoverable item, such as glass, paper, or floor tile, the evidence is transported intact to the laboratory. · If the surface cannot be submitted to the laboratory, the investigator may be able to preserve the print in a manner similar to lifting a fingerprint. · When shoe and tire marks are present at a crime scene, their preservation is best accomplished by photography and casting. · In areas where a bloody footwear impression is very faint or where the subject has tracked through blood leaving a trail of bloody impressions, chemical enhancement can visualize latent or nearly invisible blood impressions.

What is a bullet wipe?

· Bullet wipe consists principally of soot, deposited on the surface of the bullet as it moves down the barrel, which is rubbed off the bullet by the skin or clothing as it penetrates the body. In the case of revolver bullets, some of this material may be lubricant as well. In short, it is the dark ring around the perimeter of the entrance hole that's wiped off the bullets surface as it passes.

How should you handle and collect shells and casings?

· Bullets, cartridge cases, and shotgun shells recovered at the crime scene must be packaged in a properly labeled evidence container. · The obliteration of striation markings that may be present on the bullet must be scrupulously avoided. · The investigator must protect the bullet by wrapping it in tissue paper before placing it in a pillbox or an envelope for shipment to the crime laboratory.

What is the most important tool for a firearms examiner?

· Comparison microscope

Very briefly, how should you handle and collect guns?

· Firearms are collected by holding the weapon by the edge of the trigger guard or by the checkered portions of the grip. · When a revolver is recovered, the chambers, their positions, and corresponding cartridges must be recorded. · Before being sent to the laboratory, all precautions must be taken to prevent accidental discharge of a loaded weapon. · In most cases, it will be necessary to unload the weapon. · Firearm evidence must be marked for identification (usually a tag on the trigger guard) and a chain of custody must be established.

What kinds of impressions may be taken at a crime scene?

· Impressions of other kinds, such as shoe, tire, or fabric impressions, may be important evidence.

What is the Tear pattern?

· In cases where the weapon is held in contact with or less than 1 inch from the target, a star-shaped (stellate) tear pattern around the bullet hole entrance, surrounded by a rim of a smokeless deposit of vaporous lead is usually present.

When does the smokeless deposit of vaporous lead occur?

· In cases where the weapon is held in contact with or less than 1 inch from the target, a star-shaped (stellate) tear pattern around the bullet hole entrance, surrounded by a rim of a smokeless deposit of vaporous lead is usually present.

What must you see to determine to achieve individualization that a bullet was fired from a particular gun?

· Not only must the lands and grooves of the test and evidence bullet have identical widths, but the longitudinal striations on each must coincide.

How or why can serial numbers be restored on a firearm when it has been filed off?

· Restoration of serial numbers is possible through chemical etching because the metal crystals in the stamped zone are placed under a permanent strain that extends a short distance beneath the original numbers.

Which distribution pattern of gunpowder particles and other discharge residues around a bullet hole will be present when a rifle or handgun was fired less than an inch from its victim (essentially a contact shot)?

· Star-shaped (stellate) Tear Pattern

What are striations?

· Striations are fine lines found in the interior of the barrel. · These striations form the individual characteristics of the barrel. · It is the inner surface of the barrel of a gun that leaves its striation markings on a bullet passing through it.

What is the NIBIN?

· The National Integrated Ballistics Information Network (NIBIN) is a network of database files from bullets and cartridge casings retrieved from crime scenes or test fires from retrieved firearms, often linking a specific weapon to multiple crimes.

What is the breechface?

· The breechface is the front part of the breechblock that makes contact with the cartridge in a firearm. The breech block (or breechblock) in a gun is what holds a round in the chamber, and absorbs the recoil of the cartridge when the round is fired, preventing the cartridge case from moving.

1. How is the caliber of a rifle or handgun determined?

· The diameter of the gun barrel, measured between opposite lands, is known as caliber. Picture: Cross section of a barrel with six grooves. The diameter of the bore is the caliber.

Besides the barrel, what parts of a firearm may leave distinctive markings on a shell cartridge?

· The firing pin, the breechface, the extractor, the ejector, the magazine, the clip, and the fire chamber walls may all leave distinctive markings on a shell casing.

Where does the firing pin leave a mark that is paramount to individualization?

· The shape of the firing pin will be impressed into the relatively soft metal of the primer on the cartridge case.

When does a halo of vaporous lead (smoke) deposited around a bullet hole occur?

· This is normally indicative of a discharge of 12 to 18 inches or less.

When is the presence of scattered specks of unburned and partially burned powder grains without any accompanying soot detected?

· This is often observed at discharge distances up to 25 inches (and occasionally as far as 36 inches).

What firearm shoots ammunition that cannot be traced back to the weapon?

· Unlike rifled firearms, a shotgun has a smooth barrel. · Shotguns generally fire small lead balls or pellets that are not impressed with any characteristic markings that can be related back to the weapon. Shotgun and other spent cartridge casings can be traced back to a particular gun BUT this is NEVER 100% accurate. Unlike fingerprints and other biometric measurements such markings have a substantially higher chance of having identical "twins". ASK YOUR TEACHER ABOUT THIS.

What should you do when you receive items that you suspect were involved in a shooting?

· When garments or other evidence relevant to a shooting are received in the crime laboratory, the surfaces of all items are first examined microscopically for the presence of gunpowder residue. · Chemical tests, such as the Greiss test, may be needed to detect gunpowder residues that are not visible. · The firing distances involving shotguns must again be related to test firing. · The muzzle to target distances can be established by measuring the spread of the discharged shot.

There are significant differences between the barrel of a rifle and the barrel of a shotgun. Which one allows for more accuracy and how?

· With a rifle you're firing just one bullet rather than a shot cluster, so you can get a more accurate shot. · Lands and grooves are cut into the bore of a barrel of a firearm during production to increase the accuracy of that firearm because it makes the bullet spin.

Which distribution pattern of gunpowder particles and other discharge residues around a bullet hole will be present when a rifle or handgun was fired 12 to 18 inches or less?

· halo of vaporous lead (smoke) deposited around a bullet hole. This image is 12 inches.

Which distribution pattern of gunpowder particles and other discharge residues around a bullet hole will be present when a rifle or handgun was fired less than two feet from its victim?

· halo of vaporous lead (smoke) deposited around a bullet hole. This image is 18 inches

Where do striations come from?

·If one could cut a barrel open lengthwise, a careful examination of the interior would reveal the existence of fine lines, or striations, many running the length of the barrel's lands and grooves. These striations are impressed into the metal as the negatives of minute imperfections found on the rifling cutter's surface, or they are produced by minute chips of steel pushed against the barrel's inner surface by a moving broach cutter. The random distribution and irregularities of these markings are impossible to duplicate exactly in any two barrels. Striations leave individualized marks on bullets.

What is the difference between a single-shot pistol and a revolver?

•Single-shot pistols: Fire only one round at a time •Revolvers: Feature several firing chambers within a revolving cylinder. Include swing-out revolvers, break-top revolvers, and solid frame revolvers.