FRSC515 Firearm & Toolmark ID - Final Review

Handgun

a firearm designed to be capable of being held and fired with one hand

Pistol

a handgun in which the chamber is part of the barrel. Ammunition typically loaded through the use of a magazine or individually directly into the chamber

Revolver

a handgun in which multiple chambers rotate in line with the barrel. Ammunition. Loaded into the chambers of the cylinder

Hammer Fired

a separate component of the firing mechanism which uses the energy from released spring tension to strike the firing pin or primer (hammer mounted firing pin); spring tension energy to strike hammer; separate from firing pin

Striker Fired

a firing pin under spring tension or a separate component which impinges on the firing pin; striker moves itself forward under its own spring tension and hits primer

Detachable Box

a removable magazine for reloading purposes; used in pistols and some rifles

Tubular

tube shaped magazine, often attached under the barrel, where the cartridges/shotshells are arranged end to end; used in rifles and shotguns

Cycle of Fire

1. Loading

2. Chambering

3. Firing

4. Extraction

5. Ejection

Long Gun

any firearms fitted with a stock and designed to be used while held with both hands and supported by the shoulder

Rifle

a firearm with a rifled bore designed to be fired from the shoulder

Shotgun

a long gun designed to be fired from the shoulder, typically having a smooth bore (don’t have rifling) and designed to fire shotshells

Common Types of Rifles

Semiautomatic, Bolt Action, Lever Action

Single Action

Action requiring the manual cocking of the firing mechanism; one action is cocking

Double Action

Action in which a single pull of the trigger cocks and releases the firing mechanism; two actions are cocking and releasing

Hybrid Action

Slide partially cocks action and trigger further cocks and releases hammer or striker; incorporates both single action and double action

Trigger Pull

addresses the amount of force to pull trigger rearward; measured in pounds

Semiautomatic

an action in which each pull of the trigger results in a complete firing cycle. It is necessary that the trigger be released and pulled rearward for each shot fired

Blowback Operated

the barrel of the firearm fixed to the frame and the weight of the slide and tension on the recoil spring keeps the breech closed during firing

Recoil Operated

the barrel of the firearm not fixed to the frame and the slide and barrel travel/lock together for a portion of the recoil

Gas Operated

mechanism uses the propellant gases to unlock the breech and complete the cycle of extracting and ejecting

Safeties that may be Available on Pistol

1. Manual “thumb” safety

2. Manual grip safety

3. Disconnect safety

4. Key lock safety

5. Loaded chamber indicator

6. Firing pin block

7. Drop safety

8. Manual trigger safety

9. Chamber witness hole

10. Cocking indicator

Common causes of malfunctions concerning ammunition

1. Corroded ammo

2. Bad primer

3. “Squib,” underpowered load

Common causes of malfunctions concerning human error

“Limp wristling,” inadequate grip

Common causes for malfunctions concerning mechanism problems

1. Weak recoil spring

2. Weak extractor

Accidental Discharge

typically involves the discharge of a firearm without the trigger being pulled; dropped firearm, malfunctioning firearm

Unintentional Discharge

involves the trigger being pulled without the intent to fire; fault of the handler

Common types of malfunction

Failure to feed, double feed, failure to extract or eject

Function testing may include…

1. Determining if the firearm is in mechanical condition

2. Restoring an inoperable firearm to operating condition

3. test firing

4. Determining if safety features are functioning properly

5. Testing scenarios for accidental discharge

6. Determining the weight of the trigger pull

Types of Revolvers

Pin type, swing out, break open (top/bottom break)

Pin Type Revolver

pin stays in the revolver and doesn’t swing out; you load and unload a one bullet at a time through the side door

Swing Out Revolver

the cylinder swings out to the side; can load and unload the chambers at once

Break-Open Revolver

the whole gun hinges open like a shotgun; opening it usually ejects all the cases automatically

Safeties that may be on a revolver

1. Hammer block

2. Transfer bar

3. Hammer rebound

Conventional Rifling

rifling with sharp, defined edges between the lands and grooves

Polygonal Rifling

rifling in which the lands and grooves have a rounded profile

General Rifling Characteristics (GRC) include…

1. Number of lands and grooves (if there’s 8 lands, there’s 8 grooves)

   1. Lands are the raised portion

2. Width of lands and grooves

3. Type of rifling

4. Direction of twist (left or right)

5. Caliber (bore diameter)

Automatic

a firearm design that feeds cartridges, fires, extracts, and ejects cartridge cases as long as the tirgger is fully depressed and there are cartridges in the feed system

Types of rifles

1. Bolt action

2. Lever action

3. Slide/pump action

Direct Impingement

gas is bled rearward to cycle the action in a rifle

Indirect Impingement

gas moves a pistol, piston cycles the action in a rifle

Common safeties on a semiautomatic rifle

1. Manual/cross-bolt safety

2. Disconnect feature

Common safeties on a lever action rifle

Lever safety (underside receiver)

Common safeties on a bolt action rifle

1. Manual safety

2. Cocking indicator

Military versions of the AR-type rifle may have a selector switch to choose between…

1. Semiautomatic

2. Automatic fire

3. Burst mode

4. Safe mode

223 Remington / 5.56×45mm cartridges are typically chambered in this common rifle design

AR type

7.62 × 39mm cartridges are typically chambered in these common rifle designs

1. AK type

2. SKS type

Types of shotguns

1. Break open

2. Slide action

3. Recoil operated

4. Gas Operated

Types of rifles

1. Lever action

2. Bolt action

3. Blowback operated

4. Gas operated

Slide/pump action

an action where a moveable forearm is manually actuated forward and rearward to open and close the bolt

Lever action

an action where the breech mechanism is cycled by the use of an external lever which is generally found below the receiver

Bolt action

a firearm in which the bolt handle is manually reciprocated by the user to cock, load, and unload the firearm; the breech closure (bolt) is in line with the bore (barrel)

Common safeties on a semiautomatic shotgun

1. Disconnect

2. Manual/cross-bolt

Common safeties on a slide-action and break-open shotgun

Manual/cross-bolt safety

Common safeties on a shotgun with external hammers

1. ¼ cock/safety notch

2. Rebounding (spring loaded) hammers

10 gauge has a smaller barrel diameter than 28 gauge

true

Choke

an interior constriction at or near the muzzle end of a shotgun barrel bore for the purpose of controlling shot dispersion

Rifles and shotguns are typically what action?

Single action

In addition to checking the chamber to determine if a firearm is loaded, what other part of a slide/pump action or lever action firearm do you need to check to ensure the firearm is unloaded?

The magazine

Gauge

the diameter of the gun’s barrel; the larger the number, the smaller the barrel; 10, 12, 16, 20, 28, 410

Ballistics

the study of how projectile moves through the air and how they behave after being fired (what happens, before, during and after)

Breechface

The area of the firearm which supports the head of the cartridge case during firing

Firing pin aperture

the opening in the breechface through which the firing pin protrudes during firing

Striated

shear marks produces when the cartridge case scrapes against this during open fire; dragged along a surface

Impressed

an outline of the firing pin aperture shape may be seen on the cartridge case; direct contact

Class characteristics of breechface marks

1. Granular

2. Arched

3. Circular

4. Parallel

5. Cross-hatched

6. Other/indeterminate

**Can be a combination, as well as also have drag

Shapes of firing pin impressions on centerfire cartridges

1. Hemispherical

2. Circular

3. Elliptical (G-lock type)

4. Rectangular

5. D-Shaped

Shapes of firing pin impressions on rimfire cartridges

1. Rectangular

2. Hemispherical

3. Circular (flat-bottomed)

Microscopic characteristics

1. Granular

2. Circular

3. Parallel

4. Smooth (uncommon)

5. Other (usually due to large defect)

Firing pin drag occurs in what type of firearms?

Recoil operated

Class characteristics

produced by the random imperfections or irregularities of tool surfaces; these marks are unique to that tool and distinguish it from all other tools

Subclass characteristics

features that may be produced during manufacture that are consistent among items fabricated by the same tool in the same approximate state of wear; these features are not determined prior to manufacture and are more restrictive than class characteristics

Pattern matching

the act of visually comparing the surface contours of two or more striated or impressed toolmarks for corresponding and/or differentiating features

Rimfire

a self contained assembly of three components; (1) bullet, (2) cartridge case with an internal primer in its rim, (3) propellant powder

Centerfire

a self-contained assembly of four components; (1) bullet, (2) cartridge case, (3) propellant powder, (4) primer

Shotshell

a self-contained assembly of five components; (1) shot/slug, (2) hull (cartridge case), (3) propellant powder, (4) primer, (5) wad

Lead round nose (LRN)

a bullet formed in a lead alloy

Full metal jacket (FMJ)

a projectile in which the bullet jacket encloses the entire bullet, with the acception of the base

Total metal jacket (TMJ)

a bullet whose core is completely encased with copper jacketing or thick copper plating

Jacketed hollow point (JHP)

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

Semi-jacketed hollow point (SJHP)

a projectile with a partial jacket, exposing a lead nose which has a cavity

Semi-jacketed soft point (SJSP)

a projectile with a partial jacket, exposing a lead nose

Wadcutter (WC)

a bullet having a full-caliber flat nose, intended to cut a clean hole in the target for easier scoring; good for target shooting because the tip of the bullet is flat and will leave a visible hole

Semi-wadcutter (SWC)

a projectile with a distinct, short-truncated cone at the forward end

Centerfire cartridge head types

1. Rimmed

2. Semi-rimmed

3. Rimless (typically seen in pistols)

4. Belted

5. Rebated

Centerfire cartridge body designs

1. Rimless bottleneck

2. Semi-rimmed, straight

3. Rimmed, tapered

Propellant

in a firearm, the chemical composition that generates gas when ignited by the primer; the gas propels the projectile(s); also known as gunpowder

Black powder

• the earliest form of propellant

• first used in firearms in the 14^th century

• it is a mechanical mixture of potassium nitrate (saltpeter), charcoal, and sulfur in approximately the following proportion: 75% potassium nitrate, 15% charcoal, and 10% sulfur

Smokeless powder

• a propellant containing mainly nitrocellulose (single bas) containing mainly nitrocellulose and nitroglycerin (double base)

• smokeless powder comes in several firms, such as tubular, ball, and flake.

Bullet

a non-spherical projectile for use in a rifled barrel; weight is usually 7,000 grains (1 pound)

Main ingredients in primer

1. Lead styphnate

2. Antimony sulfide

3. Barium nitrate

Birdshot

pellet diameters from .050 to .230 in. (12 shot to FF)

Buckshot

pellet diameters from .240 to .360 in. (No. 4 Buck to 000 Buck)

Slug

single spherical or elongated projectile fired from a shotgun

Wad

a felt, paper, cardboard, or plastic component used in shotshells for various purposes such as filler, shot/barrel protection, powder and pellet separation

Pellets and slugs are made from the following materials:

1. Lead alloy

2. Bismuth alloy

3. Soft steel

4. Rubber (law enforcement)

Caliber

a numerical term, without the decimal point, included in the cartridge name to indicate the bullet diameter

Barrel

the part of the firearms through which a projectile or shot charge travels under powder gases; may be rifled or smooth

Action

the working mechanisms of the firearms (how firearm loads, fires, and unloads)

Range of conclusions

1. Identification

2. Inconclusive

3. Elimination

4. Unsuitable

What types of marks are routinely used for identifying a cartridge case as having been fired in a particular firearm?

1. Breechface marks

2. Firing pin impressions