Ballistics describes the behavior of a projectile before, during, and after flight. Using precise terms helps shooters, instructors, armorers, and evaluators communicate without confusing weapon function, trajectory, and terminal performance.
The three branches of ballistics
- Internal ballistics: events from ignition until the projectile exits the muzzle.
- External ballistics: projectile flight after it leaves the muzzle and before impact.
- Terminal ballistics: the projectile’s interaction with a target or medium after impact.
Firearm and cartridge terms
- Bore
- The interior of the barrel forward of the chamber.
- Chamber
- The portion of the firearm that supports the cartridge for firing.
- Throat
- The transition area from the chamber toward the rifled bore.
- Muzzle
- The end of the barrel from which the projectile exits.
- Grain (gr)
- A unit of mass commonly used for bullets and propellant. One pound equals 7,000 grains.
- Pressure
- Force per unit area produced by propellant gases. Published pressure values depend on a defined test method and should not be treated as interchangeable without context.
Lines and trajectory
- Line of bore
- An imaginary line extending through the center of the bore.
- Line of sight
- The straight viewing line through a sighting system toward the point of aim.
- Trajectory
- The projectile’s curved flight path under gravity, aerodynamic drag, and other influences.
- Time of flight
- The elapsed time between muzzle exit and arrival at a specified distance.
- Maximum ordinate
- The greatest height of the trajectory above a stated reference line, often the line of sight.
- Zero
- The sight setting and conditions under which the point of aim and the projectile’s point of impact coincide at a chosen distance.
External influences
- Velocity
- Projectile speed in a specified direction, normally reported at the muzzle or a stated distance.
- Ballistic coefficient
- A model-dependent measure used to describe how a projectile retains velocity relative to a reference projectile.
- Wind drift
- Lateral displacement caused primarily by wind acting during flight.
- Drop
- Vertical displacement caused by gravity relative to the bore line; do not confuse it with the projectile’s position relative to the line of sight.
Terminal-performance terms
- Kinetic energy
- Energy of motion, calculated as one-half mass multiplied by velocity squared. It is one measurement, not a complete prediction of terminal effect.
- Momentum
- Mass multiplied by velocity. Like energy, it describes part of the event but does not alone determine penetration or damage.
- Penetration
- The distance a projectile travels into a specified medium under stated test conditions.
- Expansion, fragmentation, and deformation
- Changes in projectile shape or integrity after impact. Results depend on projectile design, impact velocity, barriers, and the test medium.
Ballistic results are specific to the firearm, barrel, ammunition lot, atmospheric conditions, distance, target medium, and test protocol. Use manufacturer data, current technical references, and properly controlled testing rather than assuming one number predicts performance in every circumstance.