Chapter 16: FIREARMS, BALLISTICS AND IMPRESSION EVIDENCE

IN THIS CHAPTER, YOU WILL NEED TO UNDERSTAND THE FOLLOWING CONCEPTS:*How have firearms developed and what are their basic principles of operation*What are the differences and features of handguns, long guns and shotguns;*What is meant by ballistics and what factors affect the trajectory of a projectile;*How do gun and ammunition design affect aspects of ballistics.

16.1 : Forensic Firearms and Ballistics

INTRODUCTION

Today, firearms are by far

HISTORICAL PERSPECTIVEDevelop a rough timeline describing the development of firearms.

9th Century – China: Invention of _________________________________________

10th Century: Fire-lances vs. hand cannons How did they work? Advantages? Disadvantages?

Early 1300’s:

17th Century: Flintlock weapons

Mid-19th Century: breech-loading firearms

Define fixed ammunition:

Cartridge:

Round:

1

Breech-loading firearms no longer had to be smooth; What does scoring or rifling a firearm do fort the weapon?

The ‘main charge’ is the combustion reaction that ejects a bullet. What ignites the main charge?

FIREARM BASICS

Define firearm:

What do all firearms have in common?

The propulsive force behind a projectile (bullet, shot, etc) comes from the _______________________

____________________________________________________________________________________

To show the impact a gaseous product of combustion can have, what volume of CO2(g) can be

Produced if 1 gram of carbon were converted entirely to CO2(g)? _________________________

*This results in an enormous pressure behind the bullet

List the three basic firearm designed: 1)_________________________________________

2)___________________________________ 3)_________________________________

HANDGUNS: What are some types of handguns?

What are the advantages of a hand gun?

What are the disadvantages?

Compare the mechanics behind a Revolver, a semi-automatic handgun and an automatic handgun.

2

LONG GUNS: Refers to the length of the barrel.

Longer barrels allow these weapons to have _______________________________________________

Define rifling:

What is the advantage of rifling?

Label the land and groove in the diagram to the right.

The ‘handedness’ refers to the

______________________ of a bullet.

What is twist rate? Give examples of how it isexpressed.

How does POLYGONAL RIFLING differ from conventional rifling?

How is this process completed?

What types of firing mechanisms are available on a rifle?

3

Shotguns: Considered a ‘long gun’ but distinguishes itself by design features & the type of projectiles which are fired.

List & describe the two types of ammunition that can be used in a shotgun:

The barrel of a shotgun is different from a rifle in that is it ______________________ and usually not

________________________.

What does the ‘gauge’ of a shotgun refer to?

As gauge increases, the diameter of the barrel __________________________.

Once the shotgun pellets leave the barrel of the gun, they _______________________. The pattern

will increase in size as the distance from the gun ______________________.

Air Guns: These weapons move a projectile solely by

*The types of gases used are

What are the advantages of an air gun?

What are the disadvantages?

Ammunition

Define caliber:

How is caliber measured?

4

Ballistics

Ballistics is the study of _____________________________________________________________

Describe the three phases involved in the ballistics of a projectile (Be specific!):

Internal Ballistics:

External Ballistics:

Terminal Ballistics:

5

16.2 – Forensic Identification of Firearms

What is the definition of forensic firearms identification:

Two key pieces of information investigators usually want to know are…

1)

2)

*What happens when a suspect is linked to a shot fired?

What information can be determined from a bullet recovered from a crime scene?

Rifling Techniques: Describe how a broach cutter, a “button” and a mandrel are used in rifling:

Broach Cutter:

Button:

Mandrel:

How are land markings impressed onto a bullet when fired from a rifled firearm?

*What are stria and how to they help make fired bullets match a firearm?

6

Since it’s difficult to analyze the inside of a barrel, what is a suspect bullet compared to?

What are some reasons that two consecutively fired bullets may not match each other perfectly?

Are stria useful in shotgun identification? Why or why not?

What does the following image show?

What is the center indentation called?(Use the figures in the textbook if needed)

How can a firearm be rapidly identified or match with a casing in more recent time?

Where is the breech block/breech face in a firearm?

What type of firearms have an extractor?

Is it possible to find fingerprints on a bullet or casing?

7

Gunshot Residue (GSR)

When unreacted, solid residue and biproducts are discharged from a gun, the residue can often be found where?

What techniques are used to identify gunshot residue?

What elements are useful to identify?

As the residue moves away from the muzzle, it tends to _____________________________________________.

Knowing how residue spreads from a particular firearm can help determine what?

What do common color ‘spot’ tests detect in the GSR sample?

Why should hands of a victim be protected/bagged in a shooting case?

Why are hands a suspect tested as soon as possible? What could happen if they are not?

Serial Number RestorationWhat chemicals are used to help etch away the ‘stressed’ metal?

When are serial number not useful in solving a crime?

8

IBIS & NIBIN

What does abreveation stand for and what information is contained in that database?

IBIS:

NIBIN:

16.3 – Forensic Impression Evidence

Impression evidence arises from

What five pieces of forensic information may be determined from impressions?

1)

2)

3)

4)

5)

Positive image:

Negative image:

Describe a three-dimensional impression:

(Review visible, latent, plastic)

9

What are the steps taken to process impression evidence?

Footprints

Where might footwear evidence be located?

What databases are used to assist in identifying footwear impressions?

How are footwear impressions individualized to a specific shoe?

Tire Tracks

How are tire tracks similar to footwear impressions?

What information can you get from a its tread design?

How are tires matched to a specific tire track?

*What happens to the tire if a vehicle is used repeatedly after being associated with a crime scene?

Tool MarksTool mark comparisons are made to match striation marking, indentations, cut marks, etc. to determine if a particular tool was involved in a crime.

Bite MarksBite marks are measured and shapes are compare to match with human and non-human bites. A mark may be collected from food, gum, etc. as well.

10

11