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ACCURACY: The measure of a bullet's precision; the term describing a firearm's ability to shoot consistently where aimed.
BALLISTICS: The science which studies the behavior of projectiles in motion. Interior Ballistics concerns itself with events inside a gun from primer ignition through the projectile's departure from the muzzle. Exterior Ballistics deals with the motion of the projectile after it leaves the gun.
BORE: The inside of a firearm's barrel. In rifled firearms the bore diameter is the original dimension of the barrel before the rifling grooves are cut or swayed.
ENERGY: The capacity for doing work (transferring force). Spoken of in ballistics as Muzzle Energy or Remaining Energy. The measure of energy in ballistics is the Foot Pound.
FIRE FORM: To reform a cartridge case by firing it in a chamber of different dimensions.
FOOT-POUND (ft.-lb.): A unit of work; the energy required to lift one pound one foot.
FORM FACTOR: A multiplier (also called the coefficient of reduction) which relates the shape of a bullet to the shape of the standard projectile used to prepare a particular ballistic table.
FREEBORE: An unrifled portion of the bore in front of the chamber.
GRAIN: The smallest unit of the British and U.S. system of weights. One pound avoirdupois equals 7,000 grains.
GROOVES: Swaged impressions or cuts spiraled through a bore to rotate projectiles.
GROUP/GROUP SIZE: The distribution of bullets on a target fired with a single aiming point and sight setting. Group size is expressed as the distance between centers of the farthest holes and is most easily determined by measuring the extreme spread from outside to outside and subtracting one bullet diameter.
HEAD HEIGHT: The height of a bullet from its shoulder to the tip of its point
HEADSPACE: The fit of a cartridge in a chamber measured as the distance from breech face to that part of the chamber which stops the cases forward movement. Insufficient headspace hinders complete chambering; excessive headspace permits case stretching or separation.
LANDS: Those portions of the bore not cut away by rifling grooves.
MINUTE OF ANGLE (MOA): The arc subtended by an angle of one minute (1/60th of a degree) at any range, usually 100 yards. A minute of angle at 100 yards is 1.0471680" -so close to an inch that for all practical purposes it is considered an inch.
MUZZLE ENERGY: Food pounds of energy of a projectile at the muzzle of a firearm.
MUZZLE VELOCITY: The speed of a projectile at the muzzle of a firearm. (Industry standard is 15" from muzzle.)
NECK SIZE: To bring the neck of a case back to its original dimensions to hold a new bullet. Cases fired in the same chamber need neck sizing (residing) only.
OGIVE: The curve of a bullet's forward portion.
OVERALL LENGTH (OAL): The total length of a cartridge, measured from bullet tip to base of case.
PRESSURE: Force per unit area, measured in interior ballistics terms of pounds per square inch.
RECOIL: The rearward motion or "kick" of a gun on firing. Recoil in shooting is the practical effect of Newton's Third Law of Motion: for every action there is and opposite and equal reaction.
REMAINING ENERGY: A projectile's energy in foot pounds at a given range.
RIFLING: The spiral grooves in the bore of a rifled firearm. The rotation they impart to a projectile stabilizes in a flight.
SHOCK: The transference of the kinetic energy of a bullet to animal tissue or other mediums.
SHOULDER: The projection of a bottle necked cartridge case from the neck to the case body; or, the point at which the head of a projectile joins the cylindrical rear portion.
THROAT: Leade or freebore; the unrifled portion of the bore immediately in front of the chamber. Generally very short.
TRAJECTORY: The flight path of a projectile.
TWIST: The rate of spiral of the grooves of a rifle barrel expressed in length of barrel per revolution.
VELOCITY: The speed of a projectile expressed as distance per unit time.
ZERO: In shooting, the sight setting at which point of impact and given point of aim coincide at a given range.
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