Trajectory μCard (Constant Drop) Terms

Input Data

Altitude
Altitude at shooting conditions. This altitude is used to calculate the standard density at the entered altitude. You should enter an altitude density (in feet or meters) here. It is important to understand that this is the only value used to find the density of the atmosphere. The program assumes that whatever instrument provides the density altitude measurement takes into account all necessary variables. Temperature is not used to calculate the density since it is already taken into account in the density altitude. See Density altitude for more information.
Ballistic Coefficient
The ballistic coefficient for the bullet being used. It is almost always obtained from the manufacturer, but can also be measured. The ballistic coefficient is represents the ratio of the drag of the standard (e.g. G1 standard bullet) bullet to that of the bullet you are shooting. A ballistic coefficient of 0.100 means that your bullet has 10 times the drag of the standard bullet.
Bullet Length
The length of the bullet. When using a bullet in the library, this value is only used if the library value for length is zero (unknown).
Bullet Library
A drop down list showing all the buttons in the library. If a bullet is selected, the trajectory is run with the selected bullet. If "None" is selected, the entered BC, drag function and weight are used. Lapua bullets with "(CD)" in the description use the Drag Coefficients supplied by Lapua instead of the ballistic coefficient. Bullets with "(Litz)" in the description use Bryan Litz' BCs.
Bullet Weight
The weight of the bullet in grains (7000 grains per pound).
Caliber
The diameter of the bullet. This value is not used by the calculation, but is printed on output.
Distance to Chronograph
The distance from the firearm to the chronograph (typically midpoint) at which the velocities were measured. This value must be the same for both the high and low velocities.
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.
Drop Units
The units for which to display the ranges and windage. This value is usually related to the tick or hash marks on your scopes. The number of ranges displayed is equal to (Maximum Drop Value - Minimum Drop Value)/Drop Units, subject to range limits.
Include Spin Drift
If checked, the Litz spin drift is calculated for each range. The bullet length must be entered (even if you are using a bullet in the library) to calculate spin drift.
Line of Sight Angle
The angle between the line of sight and level ground. This value is used when shooting uphill or downhill. Value is a positive angle when shooting uphill and a negative angle when shooting downhill. This value is not used for the zero trajectory. It is assumed that the zero conditions are flat with zero line of sight angle and zero cant.
Low Velocity
The muzzle velocity measured at a low temperature. If you know the muzzle velocity for only one temperature, you may enter the same value for the low and high velocities and low and high temperatures. The program will not perform any temperature correction for muzzle velocity. NOTE: I have simulated a low temperature (32 °F) shot by cooling bullets in and ice water bath (in a sealed bag!).
Low Temperature
The temperature at which the "Low Velocity" (above) was measured.
High Velocity
The muzzle velocity measured at a high temperature.
High Temperature
The temperature at which the "High Velocity" (above) was measured.
Include Lead
Target lead is included when checked. If not checked, only drop and windage are included in the table.
Include Range Numbers
If checked an integer number is output next to the range. If not checked, only the range is printed along with drop, windage and lead (if Include Lead is checked).
Maximum Drop Value
Maximum value of drop for which data is diplayed. This usually represents the maximum (highest) hash mark or reticle on your scope.
Maximum Range
Maximum range for which drop and windage values are displayed.
Minimum Drop Value
Minimum value of drop for which data is diplayed. This usually represents the minimum (lowest) hash mark or reticle on your scope.
Minimum Range
Minimum range for which drop and windage values are displayed.
Notes
Text displayed at the top of the card. In order to keep the card small, this is the only output printed other than title and chart. Put what you need here to ensure that you know what the card is for.
Sight Height
The height of the sight (or scope) above or below from the centerline of the barrel. This is required because the bullet starts at a drop of -[Sight Height].
Sight Offset
The offset of the sight (or scope) to the left or right of the centerline of the barrel.
Temperature
A temperature used to calculate a muzzle velocity for output. This input is also used to calculate the speed of sound to find the value of the drag function. This input is not used to calculate density.
Wind Angle
The angle of the wind relative to downrange (0 degrees), 90 degrees is to the shooter's right, 180 is a head wind, and 270 degrees is to the shooter's left.
Wind Speed
The speed of the wind.
Zero Altitude
The altitude at which the firearm was zeroed. This value is used to find the atmospheric density.
Zero Height
The height of the zero point at the zero range.
Zero Offset
The offset of the bullet impact to the left (negative) or right (positive) of the target center at the zero conditions.
Zero Range
The range at which you wish the bullet to cross the line of sight. The units selected for the zero range are also applied to the "Ranges" value.
Zero Temperature
The temperature at which the firearm was zeroed. This value is used to find the muzzle velocity using linear interpolation between the high and low velocities. It is also used to find the mach number for interpolation into drag tables.
Zero Wind Angle
The angle of the zero wind relative to downrange (0 degrees), 90 degrees is to the shooter's right, 180 is a head wind, and 270 degrees is to the shooter's left.
Zero Wind Speed
Wind speed at time of zero.

Output Table

The output table contains drop and windage for each drop tick/hash value.