Firearms: Form, Function, and Physics

It is NEVER just the bullet

Ballistics Science of the travel of a projectile in flight Internal ballistics travel within the gun barrel External ballistics travel from gun muzzle to target Terminal ballistics path through the target --- Wound Ballistics motions and effects of a projectile in tissue Trajectory: The path of a projectile through air

Basic Terminology Ammunition cartridges shot shell Firearm ammunition comes in two forms: cartridges and shot shells.

Anatomy of a Cartridge Bullet/projectile Cartridge casing Gunpowder Primer contains shock-sensitive priming mixture, ignites propellant

Caliber Diameter of the bullet or barrel of weapon Given in hundredth of an inch Others measure the bullet, land or groove diameter of the barrel.

Typical Cartridge

Common Variations of Cartridges Hollow Point Soft Point Full Metal Jacket Total Metal Jacket Black Talon Armor-piercing Case lengths (short, long, magnum)

Hollow Point Bullet with a cavity at the nose to aid in expansion at impact and decrease penetration and disrupt more tissue as it travels through the target. Two interrelated purposes: to increase its size once within the target, thus maximizing tissue damage and blood loss or shock, and by remaining in the target to expend all of its kinetic energy in the target, some of which will be lost if the bullet continues through the target.

Soft Point Nose of bullet has exposed lead not covered by jacket expands like hollow point when it strikes target But slower expansion and greater penetration than hollow points

Full Metal Jacket Jacket covers all but the base of the bullet Higher velocity of bullet Less residue on bore (internal surface of barrel) limited in their capacity to expand.

Total Metal Jacket Jacket completely encases the bullet

Armor-piercing Designed to penetrate soft body armor Has center post of hardened steel or bronze Some coated with Teflon to minimize barrel wear when firing

Basic Terminology Rifling “spiral” grooves cut into the bore of a barrel . lands . grooves . bore diameter Rifling patterns vary by manufacturer Bore = internal surface of the barrel Lands the raised areas of the bore between grooves Grooves the lengthwise helix rifling (channels) in the bore Bore diameter interior diameter measured across the lands

Rifling Benefits the lands grip the bullet as it passes through the barrel and give it a rotary motion has a gyroscopic effect that increases the stability of the bullet’s trajectory (flies like a well-thrown football) greatly increased accuracy

Rifling Impressions left vs. right rotation conventional vs. polygonal Rifling can rotate to the right or left many types of rifling conventional uses perpendicular cuts to form grooves, forming a sharp edge profile polygonal rifling is characterized by grooves with rounded edge profile conventional vs. polygonal

Firearm Types Hand guns Revolvers Pistols Long guns Rifles Shotguns

Revolvers

Pistols

Rifles Long barreled gun Rifled barrel Types single shot bolt action pump action self-loading

Rifles

Ammunition Types Rifle generally longer than hand gun cartridges aerodynamic, pointed bullet greater velocity longer range

Firing a Gun The firing pin strikes the primer The priming compound explodes producing a high temperature jet of flame that passes through the flash hole igniting the propellant The propellant burns at a high speed and produces a large volume of gas

Firing a Gun Internal Pressure when propellant burns, most of it turns into gas (CO2 and water vapor) at first, gases are confined within the casing, and pressure is exerted equally on all surfaces (base & walls of cartridge and base of bullet)

Internal Pressure once the bullet begins to move, the volume filled by the gases increases and the pressure begins to decrease compensate by using moderated grains, increasing the rate of burning as the propellant is consumed thus internal pressure does not drop so drastically once the bullet begins to move

Rifles vs. Handguns Bullets fired from a rifle will have more energy than similar bullets fired from a handgun more powder can be used in rifle cartridges rifle bullet chambers are designed to withstand greater pressures (70,000 psi vs. 40,000 in handguns)

Rifles vs. Handguns Rifles are more accurate than hand guns longer barrel increases distance over which the bullet accelerates rifle bullets have greater velocity longer barrel also allows more time to impart the gyroscopic spin, creating a faster spin and more stable flight