Trajectory Card Terms

Input Data

Altitudes
A comma separated list of altitudes. These altitudes are used to calculate the standard density at the entered altitude. You should enter altitude densities (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.
Caliber
The diameter of the bullet. This value is not used by the calculation, but is printed on output.
Cant Angle
The angle of the tilt of the firearm to the right or left from vertical. Positive angles are to the right. 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.
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 drop outputs. For units of MOA, enter "1.0" and select "MOA" for the units. To match a scope turret unit, enter the value and units. For example, a scope that has click units of 1/4 MOA, enter "0.25" and select "MOA" for the units.
Include Only Notes in Header
If checked, only the "Notes" are displayed at the top of the output. All other inputs are not printed in the header. This makes the output more compact.
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.
Notes
Text displayed at the top of the card. Typically used for firearm description.
Ranges
A comma separated list of ranges. The output includes a bullet drop and windage for each temperature, altitude combination at each range. Units of ranges are the same as for the zero range.
Round Output to Whole Numbers
Removes any part of the drop, windage or lead after the decimal point. This is useful when your drops match the scope click settings and you want the output to be in number of clicks.
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.
Show Drop and Windage Deltas
If checked, only the differences in drop and windage from the zeroed trajectory are printed on output. Differences are in units of "Drop Units" and "Windage Units". This option is most useful when you know the bullet drop and windage for your load at some condition and you want a table of corrections.
Target Relative Drops
Calculates the bullet drop relative to the target and not the line of sight. These values are only different when the cant angle is non-zero.
Temperatures
A list of temperatures 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. Output includes a drop and windage for each temperature-altitude combination.
Windage Correction for Zero Range
If checked, the windage is changed to make the bullet cross the line of sight at the zero range -- zero windage at the zero range.
Windage Units
Same as for Drop Units, but for the windage values.
Wind Speed
The speed of the wind.
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.
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 Speed
Wind speed at time of zero.
ZeroWind 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.

Output Data

Ballistic Coefficient
The entered ballistic coefficient
Bullet Weight
The entered bullet weight
Caliber
The entered bullet diameter
Cant Angle
Entered cant angle
Drop Units
Units used for bullet drop
Line of Sight Angle
Entered line of sight angle
Show Drop and Windage Deltas
If "Yes", the table shows the drop and windage differences from zero range. If "No", actual drop and windage values are shown.
Sight Height
Entered sight height
Sight Offset
Entered sight offset
Windage Correction for Zero Range
If "Yes", the table was calculated with the correct windage angle to make the windage value zero at the entered zero range. If "No", then windage was not corrected.
Wind Angle
Entered wind angle
Wind Speed
Entered wind speed
Windage Units
Units used for bullet windage
Zero Altitude
The entered zero conditions altitude. This value was used to calculate the density at zero.
Zero Height
The entered zero height.
Zero Offset
The entered zero offset.
Zero Range
The entered zero range at the zero conditions
Zero Temperature
The entered zero conditions temperature. This value was used to calculate the muzzle velocity and mach number at zero conditions.

Output Table

The output table contains drop and windage (or drop and windage deltas) for each range, temperature and altitude combination. To find the bullet drop, find the altitude closest to the actual shooting conditions. Under that altitude, find the temperature closest to the shooting conditions. Under that temperature, go down to the range for which the drop and windage are desired. The bullet drop (or delta) is in the top of the row, the windage on the bottom.