What are firearms?  A weapon, especially a pistol or rifle, capable of firing a projectile and using a highly flammable charge as a propellant.

3 Main Types of Firearms:  Rifle  Pistol  Shotgun

Basic Handgun and Rifle Cartridge Terminology 1.Cartridge:made up of a brass case that holds the primer, powder and bullet. 2. Bullet:the projectile which is forced from the barrel 3. Flash Hole: When a primer is ignited the spark released goes through this small opening towards the gunpowder

also known as ‘propellant’ or ‘gunpowder’. Found inside the casing itself; highly reactive/flammable – but does not explode – rather it forms gases as it burns which push the bullet out of the cartridge and gun barrel. 4. Powder: 5. Primer: a pressure sensitive chemical compound that ignites when struck by firing pin of gun; detonates the propellant in a cartridge

Holds the bullet, primer, and powder; 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 across the bullet, usually expressed in hundredths of an inch (.45 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 6 – 9 large round metal pellets; ideal for larger game. (often used by law enforcement)

made up of plastic and brass housing shot, wad, powder and primer 9. Shell casing: 10. Wad: made of plastic or paper; separates the powder from the shot; holds shot together as it is projected through the shotgun barrel

11. Powder:same as above 12. Primer:same as above

How Modern Firearms work  All modern firearms use a contained and controlled explosion to create force that pushes a projectile from a barrel.  Modern firearms use cartridges or shells as ammunition.  A cartridge consists of four parts  Case  Powder (propellant)  Primer  Bullet

Cut away view of a cartridge

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 expanding gases, which finally propels the bullet

After the trigger is pulled

Rifling and bullet Stabilization

When the bullet is pushed from the case the gases that force it down the barrel cause the bullet to expand into the lands and grooves of the barrel. This forces the bullet into a spiral motion that helps to stabilize the bullet and keep it from tumbling. This in turn maintains the trajectory of the bullet and causes a straight shot.

Shotguns Shotguns do not have rifling in the barrels and use a different type of projectile Slugs generally have a rifled projectile Shot is measured by size and is shot using a “choke tube” that controls rate of expansion prior to the exit of the barrel.

Forensics of Firearms How can we use this information about firearms in forensics?

Forensics of firearms As you know, when a bullet is fired through a rifled barrel, the bullet expands into the lands and grooves. This leaves a distinct pattern on the surface of the bullet. This pattern is much like a fingerprint and is unique to the firearm the bullet was fired from.

Forensics of firearms Also, when firing pins strike the primers of shells/casings the indention that is left behind is unique to that particular firearm. Much like a fingerprint is unique to each person. These bullet/rifling characteristics and case/firing pin indentions can be used to link firearms to crimes in order to solve them.

Questions?