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What is Forensic Ballistics? Forensic ballistics is the scientific analysis or interpretation of all ballistic related evidence with the purpose of interpreting and establishing the facts in a shooting related crime Related evidence includes • firearms or guns • bullets • cartridge cases
The most common types of crime scene evidence includes • bullet holes • bullet damage on various mediums • bullet trajectories • gunshot wounds
Forensics Ballistics is divided into 3 sub-categories (a) internal (b) external (c) terminal ballistics
Internal Ballistics The study of the processes occurring inside a firearm when a shot is fired. It includes the study of various firearm mechanisms and barrel manufacturing techniques; factors influencing internal gas pressure; and firearm recoil
The most common types of internal ballistics are: • examining mechanism to determine the causes of accidental discharge • examining home-made devices (zip-guns) to determine if they are capable of discharging ammunition effectively • microscopic examination and comparison of fired bullets and cartridge cases to determine whether a particular firearm was used
External Ballistics The study of the projectile’s flight from the moment it leaves the muzzle of the barrel until it strikes the target. The 2 most common types of external ballistics examinations are: (a) the calculation and reconstruction of bullet trajectories (b) establishing the maximum range of a given bullet
Terminal Ballistics The study of the projectile’s effect on the target or the counter-effect of the target on the projectile The ‘target’ can be any solid or liquid object, but when the target is a human or animal it is common to use the term “wound ballistics”
Common types of terminal ballistics examinations are • determination of the distance between firing point and target • establishing whether or not a particular wound was caused by a fired bullet • determining the caliber and type of projectile that caused bullet damage or gunshot wound
(d) examination of bullet exit/entrance by examining the holes in targets, or the wounds in biological tissue (e) examination of ricochet possibilities and fired projectiles
Basic Handgun and Rifle Cartridge Terminology • Cartridge: also called a “round”; made up of a case, primer, powder and bullet 2. Bullet: the projectile which contains the propellant or gunpowder 3. Flash Hole: when primer is ignited the gases released go through this small opening towards the gunpowder
4. Powder: also known as ‘propellant’ or ‘gunpowder’. Found inside the bullet casing itself; highly reactive/flammable – but does not explode – rather it forms gases which push the bullet out of the cartridge and gun barrel. 5. Primer: a volatile chemical compound that ignites when struck by firing pin of gun; detonates the propellant in a cartridge
is left behind and is NOT propelled (only bullet is) when gun has been fired 6. Casing: 7. Caliber: the diameter of the bore of the bullet measured from end to end, usually expressed in hundredths of an inch (0.22 cal) or in millimeters (9 mm)
Basic Shotgun Shell Terminology 8. Shot: may be a single metal projectile – this is called a ‘slug’ (ideal for hunting large game), or the shot may contain many numerous round metal pellets (ie. birdshot or buckshot). Birdshot contains between 20 – 100 small metal pellets (ideal for hunting birds), while buckshot contains between 7 – 9 large round metal pellets (used by law enforcement)
9. Shell casing: made up of a shot, wad, powder and primer made of plastic or paper; separates the powder from the shot; holds shot together as it is projected through the shotgun barrel 10. Wad:
11. Powder: same as above 12. Primer: same as above
Bullet Designs • It is easier to design features that aid deceleration of a larger, slower moving bullet in tissues than a small, high velocity bullet. • Such measures include shape modifications like round (round nose), flattened (wadcutter), or cupped (hollowpoint) bullet nose.
Round nose • Round nose bullets provide the least braking, are usually jacketed, and are useful mostly in low velocity handguns.
Wadcutter • The wadcutter design provides the most braking from shape alone, is not jacketed, and is used in low velocity handguns (often for target practice). • A semi-wadcutter design is intermediate between the round nose and wadcutter and is useful at medium velocity.
Hollowpoint • Hollowpoint bullet design facilitates turning the bullet "inside out" and flattening the front, referred to as "expansion" or “mushrooming” • Expansion reliably occurs only at velocities exceeding 1200 fps, so is suited only to the highest velocity handguns.
Gunshot Injuries • The seriousness of gunshot wounds depends on 5 factors • kinetic energy of the bullet • distance to the target • type of tissue • tumbling (flipping around or going straight through) • bullet design ex. hollowpoint, vs. round nose etc.
Tissue - the more dense the tissue the greater the damage (will create permanent cavity) ex. muscle is more dense than lung tissue - the more elastic the tissue the less damage because will NOT create a permanent cavity ex. muscle tissue is more elastic than organ tissue
What is Gunpowder Residue? Gunpowder residue is composed of 2 substances (a) propellant (b) primer
Propellant • - 2 types of propellants are black powder or smokeless powder • Black powder • consists of 15% charcoal, 10% sulfur, and 75% potassium nitrate • when ignited, it produces a lot of smoke Smokeless powder • contains either nitrocellulose alone or nitrocellulose mixed with nitroglycerine • these compounds are known as nitrates
Primer The cartridge also contains some special chemicals called the primer These chemicals have the special property of igniting when subjected to great pressure Several types of primers may be used, but the most commonly used are lead azide, lead styphnate, mercury fulminate, barium nitrate, potassium chlorate and antimony sulfide.
How do the Propellant and Primer mixtures cause a gun to fire? When the trigger of a gun is pressed, the firing pin strikes the cartridge at a point where the primer is kept. This causes the primer to ignite. The flames thus produced ignites the propellant charge. The burning of the propellant charge produces large amounts of gases, which finally propels the bullet
