forensic investigation - ballistic

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  • Created by: aarafa11
  • Created on: 25-01-20 20:56
FIREARMS INVESTIGATION INVOLVES
What kind of weapon was used?•Was the weapon in proper working order?•How far away was the bullet fired?•In what direction was the weapon fired?•Did a specific weapon fire a bullet?•Did a particular person fire the weapon?
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Comparison and testing of
firearmsbulletscartridges
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categories of group weapons
Handguns •Rifles •Shot guns•Combination weapons (shotgun / rifle combinations)•Sub – Machine guns•Assault Rifles •Machine guns and heavy machine guns
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handgun and pistol category
single shot pistolsrevolving pistol or ‘revolver’self loading pistol
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what does the term automatic handgun
action will continue to operate until the finger is removed from the trigger or the magazine is empty.
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a true self loading pistol feature
eject the spent cartridge case after firing and then load a fresh round of ammunition into the chamber. fire the fresh round, the pressure on the trigger has to be released and then re-applied
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Single Shot Pistol features
.22 calibre made for target practice.•The barrel is hinged to the gun frame - once unlocked the barrel swings down to change the cartridge
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Revolving Pistol (Revolver) features
supply of ammunition is in a cylinder (rear of the barrel). each round having its own chamber. Cocking rotates the cylinder to bring the new round in line with the barrel. Pulling the trigger drops the hammer and fires the round
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what kind of mechanism does a revolving pistol have
single or double action mechanisms
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how to use a self loading pistol
ammunition is contained in a removable spring loaded magazine. barrel of the weapon is surrounded by a slide (integral breech lock). Pulling back slide allows the topmost round to present itself to the rear of the barrel & round pushed into chamber
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rifles categories
Single shotBolt actionSelf loadingPump action
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Single Shot rifles
barrel is hinged to the frame allowing the barrel to be dropped down for loading and unloading
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Bolt Action rifles
turning bolt slides in an extension to the barrel. Pushing the bolt forwards brings the bolt face into contact with breech end of the barrel. Turning the bolt then locks it into place. are normally magazine fed
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assault rifles
Short, light weight weapon•Fires a cartridge of lower power than a standard long barrel rifle but more powerful than can be used in a submachine gun.•AK47 or an M16 are classic examples
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shot gun
Short-range shoulder weapon•Fires small balls of metal contained in a cartridge.•Same firing action as rifles •Can have single/ double barrelled formats. •When double barrelled, the barrels can be positioned one on top of each other/ side by side
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Sub – Machine guns
categorised as fully automatic weapons.Can have a single shot feature (so you can chose how to use them)
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advantages of investigating firearms
No two firearms, even of the same make and model, will produce the same unique marks on fired bullets and cartridge cases
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Primary feature of firearms that examined for forensic analysis is rifling
Grooves cut in a spiral, lengthways down the barrel of a firearmImpart spin on bulletsLands = raised areas between two grooves
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RIFLING PATTERN IS DETERMINED BY
Counting the number of land and groove impressions around the bullet circumferenceDirection of twist: Left or Right
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MEASURING RIFLING IMPRESSIONS
MicrometerMeasuring is important as barrels with the same rifling pattern can have lands and grooves of a different width.
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investigating cartridges
Consists of cartridge case, primer and propellantCartridge designation: usually includes numerical value to indicate the calibre of the bullet and the manufacturer’s name
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PROBLEMS WITH USING RIFLING IMPRESSIONS
Damaged bulletBullet fragment
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EXAMINATIONS CONDUCTED by
Submitted firearm is fired several times in a water tank to obtain standardsFriction from passing through the water slows bullets down and they can be collected from the bottom of the tank
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FIRED STANDARDS ARE EXAMINED FOR
Microscopic marks produced by barrelConsistency of marks to those found on evidence bulletsThis is done using a comparator microscope
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WHAT IS A A COMPARISON MICROSCOPE
Two microscopes mounted side by side and connected by an optical bridgeResulting image: bullets mounted side by side with a dividing line down the middle
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CARTRIDGE CASE IDENTIFICATION
Made of brass, steel or plastic Simply loading the cartridge into a firearm can cause unique marksMarks include impressed action marks
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Firing pin impressions
IMPRESSED ACTION MARKSInclude firing pin impressions and breech marksFiring pin impressions:Indentations created when the firing pin strikes the primer of a cartridgeManufacturing imperfections or damage = unique characteristics
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Breech marks
cartridge is discharged, recoils as an opposite reaction to the pressures generated to force the bullet down the barrelUpon recoil, cartridge strikes the breech face of the firearmBreech face: rests against head of cartridge case & holds in chambe
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Card 2

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Comparison and testing of

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firearmsbulletscartridges

Card 3

Front

categories of group weapons

Back

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Card 4

Front

handgun and pistol category

Back

Preview of the front of card 4

Card 5

Front

what does the term automatic handgun

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Preview of the front of card 5
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