Forensic exam 2 (firearms)

Types of firearms and their corresponding bullets(one word)

-shotgun: lead pellets

-pistol:rounded

-rifle:pointed

-revolver:flat top

Pistols

-semi automatic

-recoil generated when fired casing ejects and reloads automatically

-reduces time to fire continued shots

-10 bullets is the legal magazine capacity

Common calibers for pistols

-.22 to .45

-9mm (Luger)

-.40 s&w

Action category characteristics

Blowback, recoil function

Style category characteristics

-Striker

-trigger is mechanically tied to striker

Single action category

Hammer must be pulled to be cocked

Double action category

Hammer moves back and forth each time trigger is pulled

Revolvers

-semi automatic

-advantages: less expensive, most reliable

-disadvantages:limited to 6 bullets in cylinder, longer reload time

-bullets stored in cylinder

-doesn't release casings

-requires greater trigger pull

Rifles

-semi and fully automatic

-long barrel w/ butt stock

-difficult to conceal

-more accurate for longer distances, ex-snipers

-18inches

-AR 15, M16

Characteristics of a butt stock

-stability

-add on to make fully auto

Shotguns

-wood butt

-shoots large number of small pellets

-pellets create a blast

-barrel does not contain rifling

-can be sawed off

-caliber referee to as gauge

Sawed off shotgun

-barrel cut short

-reduces magazine capacity

-under 18inches more dangerous

Shotgun gauge

-how many pellets are made from a 1lb ball of lead

-smaller gauge equals larger bore diameter

-larger gauge number equals smaller diameter

-12 gauge is most common

-10,12,16,20,28

Submachine pistols

-uzi serial and Ingram

-fully automatic like a machine gun but with pistol bullets

-small and lightweight

-not very accurate at moderate distances

-effective in close quarter combat

-classified as assault and illegal weapon in CA

-hold trigger down for spray of bullets

Assault classification

Flash suppressor, folding and thumbhole stock

Common caliber in submachine pistols

9mm,.45acp,.38acp,.40s&w, 10mm auto

.22 caliber

-pistol, Rifle, revolver

- cannot tell weapon based on casing

-rim firing nit center firing

Grains

-gram of bullet divided by 0.065= grain

-weight of bullet

-unit of weight used for bullet or amount of gun powder

Accuracy factors of firearms

-barrel length

-sight

-laser

-marksman's ship

Shooting distance factors of firearms

-caliber

-powder type

-amount

-Kinetic energy

-barrel length

Stopping power factors of firearms

Shape of bullet

Round v hollow

Penetration power factors in firearms

Shape and mass of bullet

Firing mechanism

-firing pin

-extractor mark

-ejector mark

-breech face m

Hollow point bullets

-top is dropped in

-expands like mushroom on impact, creates greater wound

-penetrate shorter distances

-cannot penetrate objects like body armor

Black Gun powder

Sulfur, nitrate, potassium,charcoal

Smokeless gun powder

Explosive charge compound of nitrocellulose and or nitroglycerin

Stippling

-tiny black dots around wound, like soot

-has to be at least 3inches close to occur

-distance increase equals less dots

Jacketing

Soft lees core with harder metal jacket usually copper

Caliber

Diameter of guns internal barrel bore a s bullet diameter

Casing

Primer

Groove

Edge

Caliper

Used to measure casings and barrel

Barrel must be smaller than casing for it to spin

FMJ

Full metal jacket ammunition

Lead core and hard metal jacket

Lands

UnCut portion of barrel

Grooves

cut portion of barrel

Lands and grooves

Have to have same number of rifling which produces unique impressions on bullet

Internal ballistics

-Movements within firearm

-firing pin/impression

-rifiling on bullet/projectile

-ejector, extractor marks

External ballistics

-trajectory or relationship between the motion of the bullet in the air and impact angle

Terminal ballistics

-what happens bullet strikes target

Ricochet bullets

At a low angle into hard surface

Bounces off hard surface

Mushroom bullets

At 90 degree angle onto hard surface

Fragmental bullets

At 90 degree angle onto hard surface with shirt distance

Intact bullets

Fired onto soft surface

6R

Lands and grooves

4L

Twisted

NIBIN

-National Integrated Ballistics Information Network

-stores digital images of microscopic marks on surface of fired casings and bullets

IBIS

-Integrated Ballistics Identification System

-contacted by police crime labs

-222 sites