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Firearms (and a little Ballistics). Once upon a time... more than 1000 years ago…. the Chinese discovered black powder. Black powder, (gunpowder or smokeless powder) was considered one of the Four Great Inventions of the Chinese. Do you know the other 3?. Hmmm…….
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Once upon a time...more than 1000 years ago… the Chinese discovered black powder. Black powder, (gunpowder or smokeless powder) was considered one of the Four Great Inventions of the Chinese. Do you know the other 3?
Anyway, it wasn’t until the 14th century, that gunpowder was used in guns. The first guns were cannons – large fixed, metal devices that were better at making noise than anything else.
Eventually cannons became more accurate and useful and the idea of pushing a projectile out of a metal barrel using gunpowder became part of modern warfare. The next big step in the evolution of firearms occurred when cannons were made small enough for one person to handle.
One hand or two? Guns that needed 2 hands were called long guns. Guns that needed only one hand were called hand guns. Seems to make sense….
Where do we stand now with guns? If you watch TV you will see guns everywhere. Old Westerns, gang movies, police shows, good guy vs. bad guy stuff… you know what I mean. In reality, guns are commonly used in criminal activity. Murder or injury is a common reason to shoot someone but many times a gun is merely used to gain control over a situation. Having a gun used in armed robberies, abductions, or rape can convince any victim to comply.
Deaths from gunshots can be accidental, suicidal, or homicidal. In homicide, evidence from the gun or ammunition often proves to be the perpetrator's ‘undoing’. So, how does a gun or bullet give a perpetrator ‘away’?
Firearms Identification A discipline mainly concerned with determining whether a bullet or cartridge was fired by a particular weapon…. Not to be confused with ballistics, which is the study of a projectile in motion.
Firearms examiners also do ballistics…. Examiners commonly have to: • Analyze bullets and shell casings found at a crime scene to determine what type of weapon fired them • Help with crime-scene reconstruction by estimating the distance between the gun muzzle and the victim or by working out the trajectory of the bullets. • Match a bullet or shell casing to a particular weapon or to a sample from a different crime scene to link the two.
How do guns work? Basically, guns work by starting an explosion that sends a bullet racing out of the barrel. When you pull the trigger of a gun, its firing pin strikes a cylinder of the primer in the shell of the bullet and ignites it, causing the gunpowder in the shell to explode. The explosion pushes the bullet through and out of the gun’s barrel.
Guns are classified into 3 categories: • Handguns • Rifles • Shotguns
Handguns There are three basic types: • Revolvers – You see these in old westerns. They have that revolving cylinder thingy holding the cartridges. It fires once with each trigger pull. • Semiautomatic pistols – The magazine or clip is spring loaded holding a stack of cartridges. It fires once with each trigger pull. • Machine pistols – The pistol fires repeatedly as long as you hold the trigger down.
Here is a picture of the interior of a semiautomatic handgun.
Did you know…. Early handguns were first invented in Pistoja, a town in Tuscany, Italy. These were very ornately decorated dueling handguns often having the name of the town inscribed on them. This is where we get the name ‘pistol’ for a handgun. You wanted to know that, didn’t you?
Rifles Rifles have a lever or a sliding bolt to eject a spent cartridge and bring the next one into the firing chamber.
Shotguns Shotguns don’t fire bullets but rather shells filled with groups of pellets (shot). As the shot exit the barrel, they spread out in a circular pattern which means shotguns don’t require much aiming. Just point in the intended direction.
So, what does it mean by the term ‘caliber’ or ‘gauge’? The caliber of a weapon is a measurement of the internal diameter of its barrel. Example: A .38 caliber handgun has a barrel with a 0.38 inch barrel. The gauge of a shotgun is determined by counting the number of lead balls (matching the barrel’s diameter) that it would take to weigh one pound. Example: Twenty lead balls the diameter of a 20 gauge shotgun barrel weigh one pound. Strange system, I think.
Getting Info from the Ammo Nowadays investigators rarely find a gun at a crime scene; criminals are getting smarter. Bullets found, however, can lead to the type of gun and even the individual gun used. During the collection and handling of any crime-scene bullets, the investigator must take great care not to damage or alter them….even when a ME takes a bullet out of a body during an autopsy.
Trace evidence Bullets can have important trace evidence attached. Paint, fibers, and other materials may cling to the bullet as it passes through or ricochets off walls, doors, bricks or window screens. Sometimes small bits of flesh and blood found on a bullet can yield great DNA evidence.
Shell casings A shell casing is the part of the cartridge that remains after the powder explodes and the bullet is gone. They really take a beating but this is good news. The more marks found on them, the more info they reveal. So, what can they tell you….
Firing pin impressions - The casing shows where a firing pin struck revealing whether the shell had a primer cup (a center-fire) or had a primer around the rim (rim-fire) • Breechblock patterns – When the powder in the casing detonates, it pushes the shell backwards against the breechblock leaving an impression
Headstamps – Cartridge manufacturers stamp info onto the casing • Extractor and ejector marks – These are marks etched into the casing which come from automatic and semiautomatic weapons which seat the bullet into place or eject it from the weapon. They leave unique scratches on the sides of the shell casings.
Rifling A spinning bullet is more accurate than a bullet that does not spin. Spinning objects that are propelled forward tend to go more in a straight line. (You know…just like spinning football.) So, most guns are rifled (have spiral grooves in the barrel) to make bullets spin as they leave.
Rifling consists of lands and grooves. The high parts are the lands and the deep cut-in parts are the grooves. This is a cross section of lands and grooves. This is a bullet with rifling markings. You can see the lands and grooves.
Striations When lands and grooves grab and spin a bullet, they leave markings down the side of the bullet. They are linear and parallel to the long axis of the bullet. These striations are the heart of firearms identification.
Comparison Microscope This microscope has the ability to enlarge two objects at the same time and line them up side by side. You may think it’s easy but it takes time to ‘drive’ the microscope well. It took a while for me to learn. I wish I had one to show you. Just when you think you have skills….
Databases • IBIS – Integrated Bullet Identification System …. Records all bullets/casings inspected from any crime scene • DRUGFIRE – focuses more on shell casings but also contains bullet striation patterns • NIBIN – National Integrated Ballistics Information Network… All scanned bullets and casing from a comparison microscope are stored in here.
GSR When a gun is fired much of the explosive gases and matter don’t completely follow the bullet down the barrel. Some materials escape through openings in the weapon. The chemical and particles of these gases, called gunshot residue (GSR) clings onto the shooter’s hand, arm clothing, face, nearby walls furniture, victim, etc… basically anywhere near the shooter.
GSR Presumptive tests • Infrared photography • The Griess test – a filter paper test which when pressed over the area is then immersed in a reagent revealing GSR patterns
Chemical tests Chemical test – color changing… diphenylamine will turn blue in the presence of GSR
Aside from gunpowder… • Paper making • Printing • The compass
