Firearm and Toolmark Identification: Part 1

Question 1

What is Ballistics?

Answer 1

Ballistics is the study of projectiles in motion and is usually subdivided into three parts:
* Interior Ballistics
* Exterior Ballistics
* Terminal Ballistics

Question 2

What is interior ballistics?

Answer 2

The branch of ballistics dealing with all aspects of the combustion phenomena occurring within a gun, including pressure development and motion of the projectile along the bore of the firearm.

Question 3

What is exterior ballistics?

Answer 3

The branch of applied mechanics which studies the motion of a projectile from the muzzle of a firearm to the target.

Question 4

What is terminal ballistics?

Answer 4

The branch of ballistics which deals with the effects of a projectile’s impact on the target.

Question 5

What is Firearm Identification?

Answer 5

Firearm Identification is a discipline of forensic science which has as its primary concern to determine if a bullet, cartridge case or other ammunition component was fired by a particular firearm (AFTE, 2015).

Question 6

What is Scientific Definition of a Tool?

Answer 6

Two objects which when brought into contact with each other, results in the softer object being marked. (Glossary of the Association of Firearm and Tool Mark Examiners)

Question 7

Is a firearm considerd a tool?

Answer 7

Yes. The firearm is harder than the ammunition it fires.
* The firearm marks the ammunition it comes in contact with it.

Question 8

When a cartridge is fired, what are the factors that contribute to the permanent deformation of the metal cartridge case?

Answer 8

The stress created by the Pressure generated during discharge in combination with the interaction of the cartridge case and various parts of the firearm will permanently deform the metal cartridge case.

Question 9

Explain the concept of how tool marks on both fired and unfired ammunition components are created.

Answer 9

Toolmarks on fired and unfired ammunition components are created as various firearm parts interact with the ammunition components.

Question 10

What kind of tool marks are created on firearm parts during manufacture, and what part of the manufacturing process can have an effect?

Answer 10

Tool marks on firearm parts are generated at random during manufacture, each part manufactured will contain microscopic faults that are unique to each part manufactured.

Question 11

What is the starting material, and what is its typical hardness on the Rockwell scale?

Answer 11

The manufacturing process starts out with a steel bar which usually has a hardness of 25 to 35 on the Rockwell scale so that is strong enough to maintain the pressure for the expanding gases.

Question 12

What is the drilling process ?

Answer 12

The first step involves deep hole drilling of the steel bar, creating a hole that is usually smaller than the intended calibre.

Question 13

What is the reaming process and its purpose?

Answer 13

The reaming process is used to expand the bore to the desired size and smooth the surface for a finer finish.

Question 14

What is rifling?

Answer 14

Rifling is the process of cutting grooves into the barrel of a firearm to make the bullet spin as it exits the barrel, which improves accuracy.

Question 15

What is the purpose of rifling?

Answer 15

The purpose of rifling is to spin the bullet as it exits the barrel which stabilizes the bullet’s flight and improves accuracy.

Question 16

How can rifling be achieved?

Answer 16

Rifling can be achieved as either a metal cutting, or cold forming process.

Question 17

Common types of rifling?

Answer 17

1. Button rifling
2. Single point cut rifling
3. Broach rifling
4. Hammer forging.

Question 18

What is conventional cut rifling?

Answer 18

The conventional cut rifling also known as the single point or hook rifling method is the oldest method of rifling in which a cutter is adjusted to make a single cut of approximately .0005” depth and is then pulled through each groove in the barrel.

Question 19

Explain the process of cut rifling, a method used in the manufacturing of firearm barrels

Answer 19

This is a metal cutting process that uses a carbide “hook” to cut a single groove in the barrel. The cutter is adjusted to make a cut and is then pulled through each groove in the barrel.

Question 20

Why may the cut rifling process be repeated?

Answer 20

The cut rifling pulling through process is repeated until the desired depth of the groove is obtained.

Question 21

What is broach rifling?

Answer 21

Broach rifling is a barrel manufacturing technique wherein a series of twenty-five individual cutting edges, called buttons, are used to cut each groove in a barrel at a set depth

Question 22

How many passes through the barrel with the cut rifling tool is equivalent to one pass with the broaching tool?

Answer 22

The broaching tool with its 25 buttons is equivalent to making multiple passes through the barrel with cut rifling.

Question 23

How do the buttons on the broach grow in diameter?

Answer 23

The buttons on the broach grow in diameter approximately .0005” with each proceeding button,

Question 24

What is the function of bore broaches?

Answer 24

Bore broaches are used to give the same type of finish on the top of the land as the groove broach gives to the groove.

Question 25

What is the difference between cut rifling and broach rifling?

Answer 25

In cut rifling, only one cut is made per groove, whereas in broach rifling, all grooves are cut at each button station.

Question 26

What are the similarities between cut rifling and broaching rifling?

Answer 26

*The buttons on the broach grow in diameter approximately .0005” with each proceeding button, which is the same amount the cut rifling tool is raised after making a cut in each groove.
* Also like the cut rifling, all traces of annular rings are removed in the groove but left on top of the land.

Question 27

What is the difference between broach rifling and button rifling?

Answer 27

Broach rifling cuts grooves into the barrel while button rifling presses grooves into the barrel.

Question 28

What material is used to make the button tool?

Answer 28

The button tool is made from solid carbide.

Question 29

What is the purpose of the larger portion of the button tool?

Answer 29

The larger portion of the button tool forces the grooves into the barrel.

Question 30

Is the button tool pushed or pulled through the barrel?

Answer 30

The button tool can either be pushed or pulled through, depending on the type of machinery used.

Question 31

What happens to toolmarks in the barrel before rifling with the button?

Answer 31

Any toolmarks that are in the barrel before rifling with the button will still be in the barrel after the rifling, although they will be smoothed considerably.

Question 32

Types of breech face markings?

Answer 32

1. Parallel
2. Cross Hatched
3. Granular
4. Smiles
5. Cicrcles
6. Smooth

Question 33

Types of firing pin shapes?

Answer 33

1. Rectangular Flat
2. Rect, Rounded
   3, Rect. Pointed
3. Square Flat.
4. Sq. Rounded
5. Cylindrical Flat
6. Cyc. Spheric
7. Cyc. Semi-Spheric
8. Cyc. Conical
9. Cyc. Turncated Cone
10. Ovale
11. Oblong

Question 34

What direction do most drag marks reside in?

Answer 34

Most Drag marks are created in 12 o’clock position