Ballistics Iron Cold Iron is master of men

Ballistics “Iron – Cold Iron – is master of men all” Rudyard Kipling

Introduction • Ballistics is the branch of applied mechanics which deals with the motion and behavior characteristics of missiles and of accompanying phenomena • Three types: • Interior – motion of projectile in bore of weapon • Exterior – motion of projectile while in flight • Terminal – effect of projectile Rifling in the bore when it impacts of a tank gun

History • Devices used to increase the velocity of an object thrown toward an enemy included throwing sticks and slings • Even pre-scientific man was aware that increased velocity increases the effectiveness of any missile • Black powder invented by the Chinese? Or Arabs? Or 13 th century by either German or English monk • Black powder consists of a mixture of charcoal, sulfur and potassium nitrate(saltpeter)

History • One of the earliest recorded use of firearms in warfare is that of an attack on Seville, Spain in 1247 – cannons • The first shoulder weapon – capable of aimed fire only when rested on a wall or other support • Powder, ball and matches must be carried (lighting of match warned enemies, rain was a problem)

History • The first ‘gun’ capable of producing its own fire was the wheel lock. • Wheel was serrated to provide a rough surface, cock was a clamp which held a small piece of iron pyrites – rubbed against metal will produce sparks • Winding wheel put spring under stress – when released, shower of sparks lit powder

History • The flintlock was a refinement of this idea – flint struck against a sloping piece of iron – sparks lit powder. This was lighter and more dependable than wheel lock • In the 16 th century, shallow grooves called rifling was introduced to improve the accuracy of the fired bullet

History • In 1807 a powder called a percussion primer was invented that would ignite when struck by a hammer • First breech loading guns were made in the mid 1800’s • Other improvements like automatic loading (the Gatling gun), revolving pistols followed

History Time Period pre-gunpowder 14 th to 20 th century 1900 – 1918 to present Missile Velocity several hundred ft/s up to 2000 ft/s up to 4000 ft/s up to 7000 ft/s A missile having 58 ft/lbs of energy can cause casualty in man Kinetic energy of bullets is crucial in effectiveness of weapons and velocity is the single most important factor in determining a missile’s kinetic energy

A Ballistic Pendulum is used to measure the velocity of a bullet.

Forensic Ballistics • Concerned with the aspects of ballistics that are commonly used in criminal investigations • Concentrates on identification of guns and bullets, range (closeness), and residues on suspects from gunshots • Also includes estimates of distance and location of shooter (trajectories)

Handguns and Rifles

Bullets • Both handguns and rifles have bullets – single projectiles • Rifle cartridges are typically longer • Both contain a primer (to ignite smokeless powder when hammer hits), powder, and projectile or bullet

Small Arms Cartridges

Rifle Cartridges

Parts of a Rifle Cartridge

Rifling • Both rifles and handguns have rifled barrels – spiral grooves that have been cut the length of the interior (or bore) of the barrel • Rifling consists of these grooves and the metal left between the grooves – the lands • Their purpose is to impart a rotational spin to the bullet along it longitudinal axis • This has a gyroscopic effect – which stabilizes the bullet’s flight, preventing it from tumbling end over end

Rifling • ‘twist’ refers to the number of inches or centimeters of bore required for one complete rifling spiral • In modern weapons, twist is constant throughout the length of the barrel • A new form of rifling – polygonal boring – is said to increase velocity by 5 -6% but makes it difficult to identify bullets from these guns (eg. Glocks) A Glock handgun with polygonal rifling and left twist

Rifling • The direction of the rifling can be right (clockwise) or left (counterclockwise) – and can be viewed from either the muzzle or the breach end • The direction of the rifling can be used to eliminate weapons, but seldom to identify individual weapons (eg. Colt company uses left twist to almost all handguns, most other American manufacturers use right twist)

Rifling • The number of lands and grooves can also be used to help identify the weapon that shot a particular bullet • Most modern weapons have 4, 5, or 6 grooves • Some weapons have distinctive numbers – eg. 12 or 22(microgrooves)

Calibre • Caliber is supposed to be the diameter of the gun barrel measured between opposite lands • Measured to the hundredth of an inch or in mm (eg. . 22. 38 or 9 mm) • But a. 38, for example may have bore diameters from 0. 345 – 0. 365 inches

Rifling • Three methods to produce grooves: 1. Broach cutters – concentric steel rings each larger than the preceding one. As it passes through the barrel it simultaneously cuts all the grooves into the barrel at the correct depth 2. Button process – steel button or plug is forced into barrel under high pressures. This compresses the metal to create grooves 3. Mandrel rifling – rod of hardened steel with reverse impression of grooves placed in oversized barrel and hammered or rolled

Striations • Fine lines or striations are impressions of minute imperfections found of the rifling cutter’s surface or minute chips of steel pushed against the barrel’s inner surface by a broach cutter • No two barrels will have the same striation marks, even if made by the same cutter

Striations • There is no direct way to compare the inner barrel to the bullet, so test firings are done into cotton or water. • Bullets are then compared with a comparison microscope New system using special fabric to prevent bullet deformation

Trajectories - can sometimes be determined using the angle of the bullet entrance hole, richochet marks, gunpowder marks, etc.

Shotguns

Shotguns • Use shells that contain shot – small beads or pellets usually made of lead • Typical bird hunting gun because pellets spread out over distance and increase the likelihood of a ‘hit’ • Can be single or doublebarreled, side-by-side or under/over

Tungsten pellets – now often replace lead Barrels • Shotguns have smooth barrels • Generally, projectiles cannot be traced back to the gun that fired them • By weighing and measuring the diameter of the shot recovered at a crime scene, it is usually possible to determine the size of shot used – which may indicate the manufacturer of the shell

Gauge • The diameter of the shotgun barrel is the gauge • The higher the number the smaller the barrel diameter • Eg. 12 gauge has a barrel diameter of 0. 73 inches • Eg. 16 gauge has a barrel diameter of 0. 67 inches • The exception is the. 410 where the barrel is 0. 410 inches in diameter

Cartridges or Shells • In the shell, pulling the trigger serves to release the weapon’s firing pin, which strikes the primer • Primer ignites powder, which causes the ‘wad’ – made of plastic or paper to push the pellets through the barrel • The force of the explosion pushes the spent cartridge case back with force against the breechblock • The shell is impressed with the markings by its contact with the firing pin and the loading mechanisms

Typical Shotgun Shell

Automated Systems • Several agencies now have computerized matching systems for bullets and/or cartridge cases • FBI – has one of the largest – takes digital images of both bullets and cases and compares them • Not perfect – may help to identify serial killers and/or repeat offenders

Gunpowder Residues

Gunpowder • Modern ammunition is propelled toward a target by expanding gases produced by burning nitrocellulose or smokeless powder • In practice, not all the powder burns into gases • Unburned powder, partially burned powder, and smoke are propelled toward the target with the bullet or shot

Range-Handguns and Rifles • If the muzzle of the weapon is close enough to the target, this powder will be deposited on the target • Test patterns are made with the subject’s weapon and the same ammunition to see if patterns match those at the crime scene

Range- Handguns and Rifles • Even without the suspect weapon, some generalizations can be made: • If the gun was fired from less than one inch from the target – smoke-like vaporous lead appears around the bullet hole and often the hole is star shaped. Fibers are often scorched • If the gun was 12 – 18 inches from the target – a ‘halo’ of vaporous lead appears around hole • If the gun was 25 – 36 inches from the target – scattered specks of powder can be seen on target • At more than 3 feet, usually no powder residue is found on the target

Bullet Wipe • Is the dark ring often left around the entrance hole of a bullet • Contains carbon(soot), dirt, lubricant, primer and lead wiped off the bullet as it passes through the target • Can be analyzed for composition

Infrared Light • If gunpowder residues are obscured by dirt or blood, IR light can help to visualize the gunpowder • Since gunpowder is more dense than other stains, it shows up clearly

Range - Shotguns • Diameter of spread of shot is used to estimate distance from target • Up to 4 – 5 feet from the target, the shot stays as one mass only slightly larger than the bore of the barrel • After 5 feet, generally there is about one inch of spread for each yard of distance from the target • Estimates must also take into account the barrel length, the size and quantity of pellets, the amount of powder, and the choke (constriction at the end of the barrel)

Chemical Tests for Gunpowder • The classic test for gunpowder residue is the nitrite test • A product of the incomplete combustion of nitrocellulose powder • Particles are transferred to a chemically inert gelatin-coated photographic paper using a hot iron to press paper to the sample • A chemical treatment is used to visualize the nitrites – Greiss Test

Chemical Tests for Gunpowder • However, this test will show positive for a number of other substances including fertilizer and urine • Because of this lack of specificity, another chemical test is often performed • Spraying the bullet hole with sodium rhodizonate followed by a series of oversprays with acid causes lead residues to turn pink and then blue-violet

Wounds • Often, the angle of the shot can be determined by examining the entrance hole of the bullet into the body • Bullets fired from directly in front (or behind) the body will enter and the bullet wipe pattern will be round • Bullets fired from an angle will have oval wipe patterns

Entrance vs. Exit Bullet Holes in the Skull

Tracks Even if the bullet cannot be found, often casts of the wound can reveal the type of gun used

Other Imprints • Tool marks can be traced in much the same way as bullets • Tool (or any sharp instrument) can be matched to the wound or to impressions left at the scene (eg. In doors, etc) • Comparison microscope is used here in the same way to match striations

Screwdriver Impression

Other Imprints • Tire tracks and footprints can also be compared and matched like bullets • FBI has a central registry of most footwear tracks and tire treads • Often molds are made or impressions are made clearer before photography using dyes

Conclusions • Ballistic science can help criminal investigators by: • Helping to identify the weapon used • Helping to gauge the distance of the shooter from the target • Helping to judge the angle of the shot, and thus the location of the shooter • Related sciences can help to identify imprints such as tool impressions, tire tracks, etc.