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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 test The 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
