Ballistic's Glossary
We will attempt to provide definitions in laymans terms rather than scientifically precise definitions.
Ballistics
The study of projectiles (bullets) in motion.
Ballistic Coefficient (BC)
A number which represents a bullets ability to overcome air resistance. These values are It is normally expressed in decimal form as .500 which really means that this bullet is half as efficient as the model bullet. For practical purposes, the higher the number the more efficient the bullet
Bench Rest
A solid table or bench used to support a firearm, thus mimizing human error. Also a popular competitive shooting sport.
Bullet
The projectile fired from a firearm, not the whole cartidge.
Bullet Path
The location of the bullet above or below the line of sight
Bullet Stability
The tendency of a bullet to maintatin a stable attitude in flight rather than tumbling. Determined by the spin produced by the rifling, the mass and aerodynamics of the bullet.
Caliber
The diameter of a bullet, usually expressed in fractions of an inch or millimeters. Frequently used to describe to a particular cartridge.
Cartridge
A complete unit of ammunition consisting of case, powder, primer, and bullet
Chronograph
An ellectronic device used to measure the velocity of a bullet in flight.
Diameter
The width of circle.
Drag
The retarding force on a bullet caused by air resistance.
Drag Function
A mathematical representation of how the drag characteristics of a standard bullet vary with velocity. The one most commonly used in PC ballistic software is the G1.
Drift
Deviation from a projectiles path of flight caused by it's rotation or spin. Also, commonly applied to the effects of the wind.
Drop, Bullet
The distance a bullet falls due to the force of gravity, measured or calculated from the line of departure.
Elevation
The vertical ajustment of the sight to move the tajectory of the bullet to the desired point of impact.
Energy
The capactity to do work or transfer force.
Foot Pound
A unit of kinetic energy defined as the effort required to raise 1 pound 1 foot against the force of gravity.
Form Factor
A multiplier which relates the shape of a bullet to the shape of a standard bullet. Used by some ballistics software to approximate the BC of a bullet based on shape.
fps
Feet per Second, commonly used measure of velocity.
Group
A term frequently used to describe the distribution of bullets on a target fired with a common point of aim and sight adjustment. Group size is expressed as the distance between the centers of the most widely spaced holes and is most easily determined measuring to the outsides of the hole and subtracting one bullet diameter.
Height of Trajectory
The highest point on the trajectory of a bullets flight.
Holdover
The distance a shooter must aim high to obtain the desired point of impact when the sight is adjusted for a lesser range.
Hydrostatic Shock
A pressure wave created by a bullet passing through animal tissue with high water content.
Keyhole
The imprint of a bullet on a target indicating that the bullet was not travelling point on at impact. Indicates instability, varies from a slight oval to a full length bullet shape.
Kinetic Energy
The energy of a bullet in flight. Numerically equal to half the mass of the bullet multiplied by the velocity squared.
Line of Departure
An imaginary line extending from the centerline of the bore.
Line of Sight
A straight line throught the sights to the point of impact.
Mass
The quantity of matter in an object, in simple terms the weight of an object. Actually equal to the weight divided by the acceleration due to gravity.
Meter
Fundamental unit of distance oin the metric system. Equal to 39.37 inches.
Mid-range Trajectory
The point in the trajectory halfway between the muzzle and the point of aim.
Minute of Angle (MOA)
Unit of measurement equal to 1/60 of a degree. Usually approximated as 1" per 100 yards, actually 1.047 per 100 yards.
Muzzle
The front or business end of the barrel.
Muzzle Energy
The foot pounds of kinetic energy a bullet has at the muzzle of a firearm.
Point Blank Range
The point blank range the distance a hunter can hold directly on the desired point of impact and expect to hit with in the vital zone of an animal.
Point of Aim
That point with which the sights are aligned.
Point of Impact
That point which the bullet strikes.
Projectile
An object in motion. In our case, a bullet in flight.
Range
Horizontal distance to the target.
Recoil
The kinetic energy generated in the firearm by the acceleration of the bullet. A measure of how hard a gun "kicks".
Retained Energy
The remaining engery of a bullet, measured in foot pounds, at a given range from the muzzle.
Sectional Density
The ratio of a bullets weight in pounds to the square of its diameter in inches.
Sight Height
The distance between the line of sight and the centerline of bore. Typically, 1.5" for a scope and .9" for open sights.
Standard Conditions
The set of atmospheric conditions, at a single altitude, used in ballistic calculations. (Sea Level, Temperature = 59F, Barometric pressure = 29.5275 in Hg, Relative Humidity = 78%.)
Time of Flight
The time it takes a projectile to cover a given distance.
Trajectory
The path of a bullet in flight.
Twist
The rate of spiral of the rifling grooves in a barrel, expessed as revolution per inches.
Velocity
The speed of a projectile, usually expressed in fps.
Wind Deflection
The lateral change in the path of a bullet due to crosswind effects. (See Drift)
Windage
The amount of sight correction applied to compensate for wind deflection.
Zero
The sight settings for which the point of aim and the point of impact coincide at a given range.
Zero Range
The range where the bullet path crosses the line of sight. Actually there are normally two zero ranges, one near the muzzle going up, the second coming back down. This second one is what is commonly referred to as zero range.
