JBM - Calculations - Ballistic Coefficient (Velocity) Terms

Input Data

Altitude

Used in estimating the atmospheric conditions. This value is not used unless the "Standard Conditions at Altitude" checkbox or the "Pressure is Corrected" checkbox is checked.

Chronograph Separation

The distance from the point of the first velocity measurement to the point of the second measurement. This is the distance between the two chronographs.

Drag function

A drag function (or G function) provides the forces on a standard bullet for which the drag function was derived. A bullet's ballistic coefficient then relates the drag on any bullet to that of the standard bullet.

Far Velocity

The velocity of the bullet at the end of the measured distance.

Near Velocity

The velocity of the bullet at the beginning of the measured distance.

Pressure

The barometric pressure. It may be corrected or uncorrected depending on the state of the "Pressure is Corrected" checkbox.

Pressure is Corrected

Check this box if the pressure entered is a corrected station pressure. If it is an absolute pressure, leave this unchecked.

Relative Humidity

Relative humidity (percent)

Standard Conditions at Altitude

When checked, the temperature, pressure and humidity for standard atmospheric conditions at the entered altitude (always 0% at standard conditions) are entered in the calculation. The standard used is the ICAO standard atmosphere.

Temperature

The measured or estimated air temperature.

Output Data

Ballistic Coefficient

The calculated ballistic coefficient for the selected drag function.

Atmospheric Density

The calculated density of the air.

Speed of Sound

The calculated speed of sound.

Time

The calculated time of flight of the bullet over the entered distance.

Note: If a ballistic coefficient cannot be found with the input values, the text "***" will be displayed for the ballistic coefficient and time of flight.