Definitions of 36 ballistics, ammunition, optics, and reloading terms — from ballistic coefficient and sectional density to MOA, MIL, twist rate, and DOPE.
Ballistic Coefficient (BC)
A measure of a bullet's ability to overcome air resistance in flight. Higher BC values indicate better aerodynamic efficiency and less velocity loss over distance.
G1 BC
A ballistic coefficient referenced to the G1 standard projectile, a short flat-base form. It is widely published, but the stated value can vary with velocity when the real bullet does not match that reference shape.
G7 BC
A ballistic coefficient referenced to the more streamlined G7 standard projectile. It often represents modern long boat-tail bullets more consistently when the bullet shape and measured G7 value are appropriate.
Muzzle Velocity
The speed of a bullet as it leaves the barrel of a firearm, typically measured in feet per second (fps) or meters per second (m/s).
Muzzle Energy
The kinetic energy of a bullet as it leaves the barrel, calculated from bullet mass and muzzle velocity. Measured in foot-pounds (ft-lbs) or Joules.
Sectional Density
Bullet weight relative to diameter, conventionally expressed as mass divided by diameter squared. It is one input associated with penetration potential; construction, impact velocity, stability, and the target also matter.
Bullet Drop
The vertical separation between a bullet's trajectory and the chosen line of sight or bore reference at a stated distance. It grows nonlinearly as time of flight increases; zero, sight height, drag, and atmosphere affect the reported value.
Wind Drift
The horizontal displacement of a bullet caused by crosswind. Depends on wind speed, bullet BC, time of flight, and wind angle.
Time of Flight (TOF)
The duration from when a bullet leaves the muzzle until it reaches the target. Longer TOF means more wind drift and drop.
Zero Distance
The distance at which a rifle's sights are adjusted so the bullet's point of impact matches the point of aim.
MOA (Minute of Angle)
An angular measurement equal to 1/60th of a degree, approximately 1.047 inches at 100 yards. Used for scope adjustments and accuracy measurement.
MIL (Milliradian)
An angular measurement equal to 1/1000th of a radian, approximately 3.6 inches at 100 yards. Used in tactical scopes for ranging and adjustments.
Click Value
The adjustment increment of a scope's turrets. Common values are 1/4 MOA or 0.1 MIL per click.
Twist Rate
The rate of rifling rotation in a barrel, expressed as one turn per inches (e.g., 1:10 means one rotation per 10 inches). Affects bullet stability.
Gyroscopic Stability
A bullet's resistance to tumbling in flight, provided by the spin imparted by rifling. Critical for accuracy and consistent flight.
Miller Stability Factor
An estimate of a bullet's gyroscopic stability from bullet dimensions, twist, velocity, and atmospheric conditions. A value near 1 is marginal; shooters commonly seek additional margin, but the estimate is not a firing guarantee.
Centerfire
A cartridge type where the primer is located in the center of the case head. Used in most rifle and pistol ammunition.
Rimfire
A cartridge type where the priming compound is located in the rim of the case. Common in .22 LR and other small calibers.
Case Capacity
The internal volume of a cartridge case, affecting the amount of powder that can be loaded and therefore velocity potential.
Powder Charge
The mass of propellant loaded into a cartridge, commonly measured in grains. It influences pressure and velocity together with the propellant, case, primer, bullet, seating depth, and firearm; use only published load data.
SAAMI
Sporting Arms and Ammunition Manufacturers' Institute - the organization that sets cartridge and chamber dimension standards in the United States.
Chamber Pressure
Pressure produced in a firearm chamber by expanding propellant gases. Standards bodies such as SAAMI and C.I.P. publish cartridge pressure limits and test methods where applicable.
Free Recoil Energy
The calculated kinetic energy of a freely recoiling firearm, commonly expressed in foot-pounds. It is useful for comparison but does not determine felt recoil, which also depends on impulse timing, firearm action and fit, recoil devices, and how the firearm is held.
Recoil Velocity
The calculated rearward speed of a freely recoiling firearm. It helps compare how quickly recoil energy is delivered, but action type, stock fit, recoil devices, hold, and other factors shape what the shooter feels.
Terminal Ballistics
The study of projectile behavior upon impact with a target, including penetration, expansion, and energy transfer.
Terminal Energy
The calculated kinetic energy remaining at impact. It is one reference input, not a standalone measure of terminal or hunting effectiveness; bullet construction, impact velocity, penetration, placement, game, and law also matter.
Ethical Range
A field limit that must account for the shooter's demonstrated accuracy, the specific bullet and impact velocity, conditions, game, shot presentation, and applicable law. It is not a fixed distance a cartridge database can determine; energy alone is insufficient.
Boat Tail
A bullet design with a tapered rear section that reduces base drag and improves BC for better long-range performance.
Hollow Point
A bullet design with a cavity in the tip that promotes expansion upon impact. Common in hunting and self-defense ammunition.
Full Metal Jacket (FMJ)
A bullet whose nose and sides are covered by a harder metal jacket around a core; many designs leave the base exposed. FMJ bullets are generally not designed for controlled expansion, but actual impact behavior depends on construction and conditions.
Coriolis Effect
The apparent deflection of a moving projectile in an Earth-fixed frame due to Earth's rotation. Its practical size depends on time of flight, latitude, firing direction, and the precision required, so there is no universal distance where it suddenly begins to matter.
Spin Drift
The horizontal deflection of a bullet caused by gyroscopic precession. Direction depends on rifling twist direction.
Point Blank Range
The distance within which a bullet will hit the target without hold-over, staying within an acceptable rise/fall zone.
Velocity Retention
A bullet's ability to maintain speed over distance, primarily determined by BC and initial velocity.
Chronograph
An instrument used to measure projectile velocity. Common designs use optical or electromagnetic sensors, while Doppler radar units track velocity without requiring the projectile to pass through sensor screens.
Ogive
The curved forward portion of a bullet from the bearing surface to the tip. Affects BC and feeding reliability.