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The Anatomy of Firearms - Forensic Science Analysis and Lab | FRSC 4253, Study notes of Forensics

anatomy of firearms Material Type: Notes; Professor: Adams; Class: Forensic Sci Analysis & Lab; Subject: Forensic Science; University: University of Central Oklahoma; Term: Spring 2011;

Typology: Study notes

2010/2011

Uploaded on 01/21/2011

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Cusack 1
01/10/2011
The Anatomy of Firearms
Purpose
oThe purpose of this module is to familiarize yourself with the anatomy of firearms
and the most common firearm types
Objectives
oThe earliest known firearm ignition systems and their anatomy and shortfalls
o3 popular ignition systems that ultimately provided the greatest milestones in
weapon and ammunition development
oCharacteristics of rifled barrels
oFirearm nomenclature
oThe most common firearm types used today and their anatomy
Brief history
oModern firearms are manufactured in a variety of shapes and sizes to fit multiple
purposes
oToday there are vast numbers and a staggering assortment of models
oIn today’s society, practically any type of gun can be found. Uses vary by youth
gangs, persons involved in drug trafficking, paramilitary “survivalists” and even
what we would considers “ordinary” citizens
oThe earliest form of a firearm was simply a small cannon (hand cannon)
oThese weapons were likely used as psychological deterrents more than anything
else
oOriginally hunting and intimidation
o3 firearm ignition types:
Matchlock
Wheel Lock
Flintlock
Expensisve
Early ignition systems
ohttp://www.hunter-ed.com/mi/course/ch5_know_your_muzzleloader.htm (photos)
Rust causes M-16 to jam
Inability to oil gun
oMatchlock and Wheel lock systems
Matchlock
Pan
Pan cover
Slow match
You actually have to light
oUnable to stay lit if wet or moist
Wheel lock
Pan
Pan cover
Pyrite
pf3
pf4
pf5
pf8
pf9
pfa

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The Anatomy of Firearms  Purpose o The purpose of this module is to familiarize yourself with the anatomy of firearms and the most common firearm types  Objectives o The earliest known firearm ignition systems and their anatomy and shortfalls o 3 popular ignition systems that ultimately provided the greatest milestones in weapon and ammunition development o Characteristics of rifled barrels o Firearm nomenclature o The most common firearm types used today and their anatomy  Brief history o Modern firearms are manufactured in a variety of shapes and sizes to fit multiple purposes o Today there are vast numbers and a staggering assortment of models o In today’s society, practically any type of gun can be found. Uses vary by youth gangs, persons involved in drug trafficking, paramilitary “survivalists” and even what we would considers “ordinary” citizens o The earliest form of a firearm was simply a small cannon (hand cannon) o These weapons were likely used as psychological deterrents more than anything else o Originally hunting and intimidation o 3 firearm ignition types:  Matchlock  Wheel Lock  Flintlock  Expensisve  Early ignition systems o http://www.hunter-ed.com/mi/course/ch5_know_your_muzzleloader.htm (photos)  Rust causes M-16 to jam  Inability to oil gun o Matchlock and Wheel lock systems  Matchlock  Pan  Pan cover  Slow match  You actually have to light o Unable to stay lit if wet or moist  Wheel lock  Pan  Pan cover  Pyrite

o Creates a spark  Cock or doghead  Spring-powered wheel  Flintlock – first time we see people say “cock the hammer”  Flint  Frizzen o Causes spark  Lock plate  Pan  percussion lock o cock o Cap o Nipple  Combustion and hot gases  3 popular systems that were breakthroughs in the history of firearms were:  The pin fire system (bad) o Primer cup o Firing pin o Cartridge case o projectile  The rim fire system - .22 caliber, short, long, long rifle - common o Hammer with firing pin o Primer o Cartridge case o projectile  The center fire system – know this drawing – one of most prominent designs o Firing pin o Priming compound o Primer cup o Cartridge case o Flash hole  What is normal versus abnormal o More and more airsoft pistols look like real things  Not taped, no neon sights  Regular consumer would not know that it isn’t a real pistol o Ruger Mark III  .22 caliber  Smaller than palm of hand, fits on a keychain  Revolver 01/12/  Smooth bore weapons

 Smooth o Looks like it just slid down the barrel o Darkening = slippage o Burns as it slides down the bullet, gases escape on edges of the rifling  Masks typical characteristics  Hard to identify  Masks individual characteristics on bullets  Cartridge cases have lots of characteristics  Mostly seen in handguns and semiautomatic pistols  Reasonably priced  Law enforcement uses o Desert Eagles o HNKs  High end semiautomatic pistol  Firearms terminology o The Association of Firearms and Toolmark Examiners (AFTE) created a glossary of terms (1977) that was to be used as reference guide for terms commonly used in the discipline. However, over time contributions have been so extensive, for the purposes of this course, we will only examine those necessary o Rifling  Term given to spiral grooves cut into the bore of a barrel  Stabilizes a bullet in flight  Improves trajectory  Caters to higher velocity  Groove Diameter  Photo Precision Forensic Testing  Groove at top to groove at bottom  Bore Diameter  From land to land, interior portion of bore o Lands  Always have equal numbers of lands and grooves  Twist left or right  Land flows over your right shoulder o Right hand twist  Land flows over your left shoulder o Left hand twist o Grooves  Always have equal numbers of lands and grooves  o Caliber  Nominal diameter of the bore within a firearm in inches (i.e. .357)  In regards to ammunition, caliber refers to nominal bullet diameter without the decimal included  European made

 9 mm  9 x 19 inches in US (.355 inches) o Action  The working mechanism of a firearm  May be broken down into action types (i.e. bolt, automatic, lever) o Projectile (Bullet)  An object propelled by force of rapid burning gases or other means  Bullet  A non-spherical projectile for use in a rifled barrel o Cartridge Case  The container that holds all components which make up a live round of ammunition o Propellant  The chemical composition within a cartridge case that produces combustion and gases propelling the projectile o Primer  The ignition component of a cartridge case o Recoil  Note: Every firearm has recoil. For every action there is an equal or similar reaction  Is the effect (mechanism) that creates a reaction due to pressure and force within a firearm  Often referred to as bite or kick  i.e. the average pressure in a .45 caliber pistol is around 14, pounds per square inch o meaning, when the pistol is fired there is a pressure over one ton pushing the bullet down and out the barrel, while at the same time pushing the gun back towards the shooter  Firearm Types o Are pellet guns, BB guns, air soft pistols, or paintball guns considered firearms? No; They don’t use combustion. Legally is a firearm, in this course, it is not a firearm.  Know the code word for word – on testThe Federal Statue Title 18, United States Code, Section 921(a)(3):(3) the term “firearm” means (A) any weapon (including a started gun) which will or is designed to or may readily be converted to expel a projectile by the action of the explosive; (B) the frame or receiver of any such weapon; (C) any firearm muffler or firearm silencer; or (D) any destructive device. Such term does not include an antique firearm. o Muffler or silence  This includes a potato o Antiques  Have to be manually lit o There are four types of firearms:  Pistol

 Parts o Genitron.com o Slide o Safety o Hammer o Frame  Only portion that contains the serial number  Considered a firearm in itself  Does not include slide connected to the body o Trigger guard o Slide release o Trigger o grips  Revolver  Background o Advantages  Simple design  Reliable  Reasonable price  Tend to be more accurate  Long barrel o Disadvantages  Limited to six shots  Slow reload  Trigger pull is greater o Firearm having multiple chambers configured around an axis o Utilize the same discharge mechanism or action to successfully discharge  Actions o Single action  Requires manual cocking of the external hammer before sufficient pressure releases the firing mechanism  Benefit o Lighter trigger pull o Releases trigger to the rear after manual cock (not the same thing as a hair trigger – not standard from manufacturer – manipulated) o Double action  An action in which a single pull of the trigger cocks and releases the external hammer  Disadvantage o Heavier trigger pull

 Parts o Genitron.com o Cylinder stop notches o Frame o Cylinder release o Hammer o Cylinder o Barrel o Ejector rod o Trigger guard o Trigger o grips  Shotgun  Background o Similar in appearance to rifles but the barrel is much larger o Do not have rifling  Smooth bore weapons o Advantage  Ability to utilize different forms of ammunition  i.e. slug, pellets, buck shot o a long arm/big bore firearm consisting of a receiver, stock, and barrel. Combinations or frames may be configures as over-under, double barrel, or hinged frame  Actions o May vary depending on style of shotgun, however actions are similar to those used in rifles  i.e. Autoloading, single action, and pump/slide action  Pump action most common style and most commonly preferred o Pump/slide action  Requiring the manual cycling of a slide located in front of the receiver to load, operate the firing mechanism, extract and eject the fired cartridge  Parts o Stock o Safety o Frame/receiver o Ejection port o Magazine o Fore-end o muzzle  Rifle  Background

 Evidence, once obtained by the examiner should be logged or booked into the laboratories evidence log, then properly stored until examined  Evidence Transfer  Once evidence has been examined and resealed, proper paperwork to complete the chain of custody log should be filled out  The evidence may then be transferred to another unit for examination or back to the property management unit for storage