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Chapter 21 – Firearms and Tool Marks
FRSC 7104Criminalistics I
Professor Bensley
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FRSC 7104 – Chapter 21 ObjectivesAfter studying this chapter, the student should be able to: Recognize the various types of firearms and their basic
components Recognize the various types of ammunition and their
uses Understand how firearms evidence is collected and
analyzed Describe the basic details of tool mark comparisons and
firing distance determinations
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FRSC 7104 – Chapter 21 OutlineI. Introduction
FBI Uniform Crime Reports (2011) Murder Victims
by Weapon, 2007–2011
2007 2008 2009 2010 2011Total 14,916 14,224 13,752 13,164 12,664Total firearms: 10,129 9,528 9,199 8,874 8,583
(68%) (67%) (67%) (67%) (68%)Handguns 7,398 6,800 6,501 6,115 6,220Rifles 453 380 351 367 323Shotguns 457 442 423 366 356Other guns 116 81 96 93 97Firearms, type not stated 1,705 1,825 1,828 1,933 1,587
Knives or cutting instruments 1,817 1,888 1,836 1,732 1,694Blunt objects (clubs, hammers, etc.) 647 603 623 549 496
Personal weapons (hands, fists, feet, etc.)1 869 875 817 769 728Poison 10 9 7 11 5Explosives 1 11 2 4 12Fire 131 85 98 78 75Narcotics 52 34 52 45 29Drowning 12 16 8 10 15Strangulation 134 89 122 122 85Asphyxiation 109 87 84 98 89Other weapons or weapons not stated 1,005 999 904 872 8531 Pushed is included in personal weapons.
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FRSC 7104 – Chapter 21 Outline
II. Firearm ExaminationsA. Types of Firearms
1. Handgunsa. Revolvers
i. Single actionii. Double action
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FRSC 7104 – Chapter 21 Outlineb. Semi-automatic pistols
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FRSC 7104 – Chapter 21 Outline
2. Rifles (Shoulder arms)
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FRSC 7104 – Chapter 21 Outlinea. Semi-automaticb. Automaticc. Machine Gunsd. Submachine Guns
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Top - .50 caliber M2 machine gunBottom - Heckler & Koch MP5 submachine gun
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FRSC 7104 – Chapter 21 Outline
3. Shotguns
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FRSC 7104 – Chapter 21 OutlineB. Firearm Construction
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FRSC 7104 – Chapter 21 Outline1. Rifling
a. Lands and Grooves
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FRSC 7104 – Chapter 21 Outlineb. Broach rifling
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FRSC 7104 – Chapter 21 Outlinec. Button Rifling
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FRSC 7104 – Chapter 21 Outlined. Hammer forged rifling
e. Electrochemical Rifling
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Bullet Impressions
Left - A bullet fired from a conventional 6/right rifled barrelRight – 40 Caliber bullet with polygonal rifling impressions like those seen
on the 40 caliber bullet
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FRSC 7104 – Chapter 21 Outline2. Caliber
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Caliber
Left to Right:.50 caliber down to .22 caliber
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FRSC 7104 – Chapter 21 Outline3. Gauge
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FRSC 7104 – Chapter 21 OutlineC. Firearm Ammunition
1. Bullets
32 S&W LONG caliber plain lead bullet
9mm LUGER caliber FEDERAL "Hydra-shok" bullet
7.62x39mm caliber armor piercing bullets
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FRSC 7104 – Chapter 21 Outline
2. Propellants3. Primers4. Cartridge Cases5. Shot shells
Video of Firing Action in a Firearm
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Plain Lead Bullet
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FRSC 7104 – Chapter 21 OutlineD. Forensic Examinations of Firearms
1. Class vs. Individual Characteristics
Land Impressions: Left - 380 AUTO caliber FMJ bullets fired from a EAA Corp. pistol Right - 9mm LUGER caliber FMJ bullets fired from a BROWNING pistol.
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General Rifling Characteristics SearchCARTRIDGE MANUFACTURER TWIST L&G LAND GROOVE
9MM LUGER AA ARMS INC R6 .055 .120
9MM LUGER ASTRA R 6 .053 .128
9MM LUGER BERETTA R 6 .055 .130
9MM LUGER HI-POINT FIREARMS R 6 .055 .120
9MM LUGER INTERDYNAMIC R 6 .055 .124
9MM LUGER LLAMA R 6 .054 .120
9MM LUGER MAUSER R 6 .054 .128
9MM LUGER SMITH & WESSON R 6 .056 .122
9MM LUGER STAR R 6 .054 .126
9MM LUGER SWD INC R 6 .055 .120
9mm LUGER bullet, fired from a 6/right rifled barrel, with a land width of .055mm and a groove width of .125mm. Firearm examiners will usually search with a plus or minus .003-.005 tolerance and the results of the search would look something like the data contained in the above table.
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FRSC 7104 – Chapter 21 Outline
2. Bullet Identification
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Bullet FragmentsImage below shows the
bullet fragments from left compared to a known standard bullet. Standard is on the left side of the comparison below.
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FRSC 7104 – Chapter 21 Outline3. Cartridge Case Identification
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FRSC 7104 – Chapter 21 Outlinea. Striated Action Marks
i. Chamber Marks
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FRSC 7104 – Chapter 21 Outlineii. Shear Marks
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FRSC 7104 – Chapter 21 Outlineiii. Firing Pin Drag Marksiv. Extractor Marksv. Ejector Marks
b. Impressed Action Marksi. Firing Pin Impressions
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FRSC 7104 – Chapter 21 Outlineii. Breech Marks
Breech face of 12 gauge shotgun and photomicrograph of cartridge case fired from the same weapon.
iii. Ejector Marks
E. NIBIN
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FRSC 7104 – Chapter 21 OutlineIII. Gunshot (Gunpowder) Residue
A. What causes gunpowder residue?
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FRSC 7104 – Chapter 21 Outline
B. Distance Estimations (Determinations)1. Ranges of fire
a. Contactb. Near-contactc. Intermediated. Distant
3” 6” 12”
24” 36”
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FRSC 7104 – Chapter 21 Outline
C. Powder Residue Detection Methods1. Visual2. Chemical
a. Griess Test (Modified Griess Test)
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FRSC 7104 – Chapter 21 Outlineb. Sodium Rhodizonate
1. Untreated 12 inches
2. Greiss Test 12 inches 3. Greiss followed by Sodium Rhodizonate
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FRSC 7104 – Chapter 21 OutlineD. Gunshot Residue on Hands
E. GSR Analysis Techniques
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FRSC 7104 – Chapter 21 Outline
F. Bullet Holes1. Entrance Wounds2. Exit Wounds
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FRSC 7104 – Chapter 21 OutlineIV. Toolmark Examinations
A. Introduction
Forged Key Toolmarks
Lock Picking Toolmarks
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FRSC 7104 – Chapter 21 Outline
B. Types of Toolmarks1. Indentations2. Striations
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FRSC 7104 – Chapter 21 Outline
C. Class vs. Individual Characteristics in ToolmarksD. Unusual Toolmark Types
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FRSC 7104 – Chapter 21 Outline
E. Collecting and Processing Toolmark Evidence1. Photography
2. Processing at Crime Scene
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FRSC 7104 – Chapter 21 Outline
3. Trace Evidence
4. Processing in the laba. Cast vs. Mold
5. Lab Examinations