Module 10

The examination process usually includes the following observations and determinations:

-Bullet weight -Composition of the bullet -Base description -Type and position of cannelures -Manufacturer/marketer-General rifling characteristics -Bullet design -Extraneous marks due to firing (skid marks/slippage, shave marks, flared base) -Suitability for comparison purposes

Wadding materials may include the following:

-Card wad -Shot collar -Over-shot wad or top wad -Under-shot wad -Filler wad -Over-powder wad -Cup wad

What two categories do most modern bullets fall into?

-Plain lead bullets ( swaged or cast) -Jacketed bullets (heavy core enclosed by an outer jacket of gilding meta(heavy core enclosed by an outer jacket of gliding metal)

How is the diameter of a shotgun defined?

-bore diameter -the interior dimensions of the barrel forward of the chamber but behind the choke.

How is the diameter of a barrel of a rifled firearm defined?

-bore diameter -the minor diameter of a barrel which is the diameter of a circle formed by the tops of the lands

The examiners report on the fired bullet may include

-descriptive information (e.g., caliber, construction, possible cartridge types, and possible manufacturer), -general rifling characteristics, -listing of possible firearms that may have produced the general rifling characteristics, -evidentiary potential based on individual characteristics present

What are the effects of firing?

-shaving(shearing) -skid marks (slippage) -flared bases of bullets -blowby -barrel leading(metal fouling) -corroded/rusted barrels -leading smears

What type of bullet is most likely composed of heavier metals?

44 Rem Magnum or bullet cores

Spitzer Bullets

A bullet design having a sharp point, long ogive, usually of seven calibers or more (i.e., ogive radius length to bullet diameter).

Jacketed Hollow Points

A bullet having a metal jacket enclosing a lead alloy core. The entire bullet is enclosed except for the nose which has a cavity.

Tracer Bullets

A bullet that has a burning compound in its base which permits observation of its flight.

Wadcutter Bullets

A cylindrical bullet design having a sharp-shouldered nose intended to cut target paper cleanly to facilitate easy and accurate scoring

Frangible Bullets

A projectile designed to disintegrate upon impact with a hard surface in order to minimize ricochet

Meplat

Blunt tip of some bullets, specifically the diameter of that blunt tip

Shotshells may be comprised of a number of components

Card (paper) or fiber disks Plastic wadding components Lead, steel, bismuth, or tungsten alloy shot pellets Shotgun slugs Shot buffer materials (granular plastic particulate)

Cannelure

Circumferential groove in a bullet generally of a knurled or plain appearance for the purpose of lubrication or identification, or to assist in crimping a bullet in the mouth of a cartridge case

Are the number, width, and direction of twist of the rifling grooves in a barrel of a given caliber firearms individual or class characteristics?

Class

Heel

Configuration of the intersection of the bearing surface and base of a bullet

Ogive

Curved forward part of a bullet

How are the weight ranges of a bullets determined/defined?

Determined by cartridge type

How is a projectile propelled out of a firearm?

Expanding gases forces the bullet out of the cartridge and down the barrel in which the rifling in the barrel causes the bullet to spin as it travels out of the barrel

What type of bullet is designed to disintegrate upon impact with a hard surface in order to minimize ricochet?

Frangible bullets

What type of bullets have a cavity in the nose to facilitate expansion?

Jacketed hollow point bullets

Using a comparison or stereomicroscope, land and groove impressions can be measured using a variety of equipment:

Micrometer Calipers Glass measuring reticule Electronic reticule Digital measuring equipment and software MP 6 optical projector (no microscope) Machinists scale

Should an analyst measure all bullet fragments together?

No because each fragment may not originate from a single bullet

There may be retrievable information if all of the following are present on a damaged bullet:

One or more measurable land impression One or more measurable groove impression Sufficient bullet remains to determine a measured caliber

Bearing Surface

Portion of the outer surface of a bullet that makes direct contact with the interior surface of a gun barrel

What are the potential diameters of .357" cartridge type?

Potential diameters à .353"-0.373"

What types of tips can a bullet have?

Silver tip, soft point, metal point, full metal jacket, hollow point, hydrashok

How is a bore diameter defined?

The major diameter of a barrel which is the diameter of a circle circumscribing the bottom of the grooves in a rifled barrel

What part of a bullet is used to measure diameter? Why?

The measured diameter of fired bullets is taken from one groove impression (a high point on a fired bullet) to a groove impression on the opposite side of the bearing surface. If there are an odd number of groove impressions, the measurement is taken from the edges of a pair of impressions.

What is the Rule of 17?

The theoretical diameter of shot is calculated as follows: Diameter of shot = 17 shot size, Where all measurements are expressed in hundredths of an inch, For example, for No. 6 shot: Diameter of shot = 17-6 = 11 (or 0.11 inches in diameter) -Note: This technique does not work for buckshot.

What calculation is used to find the theoretical diameter of a shot pellet?

The theoretical diameter of shot is calculated as follows: Diameter of shot = 17 shot size, where all measurements are expressed in hundredths of an inch. For example, for No. 6 shot: Diameter of shot = 17-6 = 11 (or 0.11 inches in diameter) Note: This technique does not work for buckshot.

What are the parts of a bullet?

Tip, meplat, ogive, nose, cannelure, bearing surface, base, heel

What are the primary physical features of bullets?

Weight, measured caliber/diameter, composition, jacket type, magnetic properties, length, color/finish, base construction, base shape, nose construction, nose shape, cannelures

Are there different degrees of bullet jacketing? If so, what are they?

Yes; Full metal jacket, semijacketed, total metal jacket

What is the standard ammunition file?

a collection of known standards

The categories of general rifling characteristics are

caliber (bore diameter), number of land and groove impressions, direction of twist, land and groove impression dimensions

The data obtained from a fired bullet provides the input data for searching the GRC file, including

caliber, number of lands and grooves, direction of twist, land and groove impression measurements, other information

general rifling characteristics

class characteristics like land and groove impressions

Incendiary bullets

contain a chemical compound that ignites upon impact, starting a fire.

Exploding bullets

contain a primer or other explosive and are designed to explode upon impact.

Armor-piercing bullets

designed to pierce metal. They usually contain a hardened core or are completely composed of a substance other than lead or lead alloy.

mushrooming

the controlled expansion of a bullet upon impact with a target. The bullet is designed to significantly increase in diameter upon impact

By examining wadding materials, the examiner may be able to determine

the gauge of the shotgun, the manufacturer or marketer, a range of possible shot sizes based on impressions in the wad, individual characteristics (in some cases)

What is the plastic, paper, or fiber disk used to keep ammunition components in place or separated?

wad