Trajectory 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.
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.
Barrel Twist
The twist length of the barrel.
Twist Direction
The twist direction of the barrel. Right is a clockwise twist when looking through the barrel from the chamber to the muzzle. Left is counter-clockwise.
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 (Use entered BC)" 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
Diameter of the bullet.
Cant Angle
The angle of the tilt of the firearm to the right or left from vertical. Positive angles are to the right.
Distance to Chronograph
The distance from the muzzle of the firearm to the chronograph used for muzzle velocity measurements. If the muzzle velocity is estimated, enter 0.0 for this value -- no correction.
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 1st Column
A drop value (the number you enter) and its associated units. Output windage for the first column are multiples of this value/units combination. See the drop units topic for more information.
Drop Units 2nd Column
Same as Drop Units 1st but for the second column of drop, windage and lead.
Elevation
The vertical angle the barrel makes with the line of sight. This value is not generally known and can be ignored if the "Elevation Correction for zero range" option is checked.
Elevation Correction for Zero Range
Or Drop correction, causes the elevation to be raised as required to cause the bullet to cross the line of sight at the zero range. Without this box checked, the zero range is ignored.
"Energy Column" Formula
Use this input to select what is calculated for "energy" column (fourth column from the right). Values include Energy in foot-pounds or Joules, momentum in pound-seconds or Newton-seconds, Taylor's Knockout Value, optimum game weight for hunting or varmint bullets and Krupp's tank formula in inches and millimeters. Krupp's tank formula gives the thickness of a sheet of mild construction steel that can be penetrated by a full metal jacketed, lead core round. It does not calculate the the penetration depth into a solid (semi infinite) block of steel.
Humidity
Relative humidity (percent)
Include Danger Space
If checked, the output will include the danger space for every calculated range.
Include Extra Rows
If checked, the output will include extra rows even if they are not an multiple of the range increment. Extra possible rows include the sound barrier crossing, zero range and maximum point blank range.
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.
Mark Sound Barrier Crossing
If checked, the output velocity background color is red for the first printed velocity that is less than the calculated speed of sound.
Maximum Range
The maximum displayed range.
Minimum Range
The minimum displayed range. Data is calculated from the muzzle the maximum range, but may be displayed from the minimum to the maximum range. (e.g. with a minimum of 990, maximum range of 1010 and a range increment of 10 you would see data 990, 1000, 1010 yards).
Muzzle Velocity
The velocity of the bullet as either (1) measured at some distance from the muzzle or (2) as estimated from reloading data. The on-line ballistics page can correct for the distance to chronograph. (The velocity lost traveling to the chronograph.)
Plastic Tip Length
The length of the plastic tip (e.g. "Ballistic Tip"). If the bullet has no plastic tip, enter zero. This value is used to implement the second version of the Miller Stability rule.
Pressure
The barometric pressure. It may be corrected or uncorrected depending on the state of the "Corrected Pressure" 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.
Range Increment
The increment used in displaying the calculated data.
Ranges in Meters
When checked, all ranges entered (minimum, maximum, increment and zero) are in meters.
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. Positive offsets are to the shooter's right. Negative are left.
Std Atmosphere 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.
Target Angle
The angle of the target speed direction with the line of sight. A 90 degree angle is a target moving perpendicular to the line of sight. This angle is given in degrees by selecting an angle from the list.
Target Height
The height of the target. This value is used in calculating the danger space.
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.
Target Speed
The speed of the target in miles per hour. This value is used to calculate running target leads. Negative speeds are to the shooters left, positive to the shooter's right.
Temperature
The measured or estimated air temperature.
Vital Zone Radius
Radius of the vital zone for which the maximum point blank range is calculated. The vital zone is defined as the area from one radius below the line of sight to one radius above the line of sight.
Windage
The horizontal (side to side) angle the barrel makes with the line of sight. This value is not generally known and can be ignored if the "Windage Correction for zero range" option is checked.
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.
Wind Angle
Angle of the wind direction. A wind blowing downrange has an angle of zero, a wind blowing to the shooter's right has an angle of 90, a headwind, an angle of 180 and a wind blowing to the shooter's left has an angle of 270 degrees.
Wind Speed
The speed of the wind.
Zero at Max. Point Blank Range
If checked, the zero range is changed to achieve the maximum point blank range.
Zero Height
The height of the zero point at the zero range.
Zero Offset
The lateral displacement the zero point at the zero range.
Zero Range
The range at which you wish the bullet to cross the line of sight.

Output Data

Atmospheric Density
The calculated density of the air.
Azimuth
The angle that the barrel makes with the line of sight in a horizontal direction -- positive to the shooter's right. This is the "lead" angle in minutes of angle for the selected zero range.
Danger Space
The minimum and maximum range near the output range for which the bullet will hit a target of the entered height. This is used as an gauge of the required range estimation accuracy.
Drop
The distance above or below the line of sight. Listed in either inches, minutes of angle or mils (6400 mils per 360 degrees or 3.375 mils per MOA). Drop is positive above the line of sight and negative below the line of sight.
Elevation
The angle that the barrel makes with the line of sight in a vertical direction. This is the "holdover" angle in minutes of angle for the selected zero range.
Energy
Kinetic energy of the bullet. The kinetic energy is a measure of the maximum amount of work (force time distance) an object can do. [It is also a measure of the work done by the firearm/case/primer/powder on the bullet.]
Lead
The required target lead to the left or right of the line of site to hit a moving target. Lead is positive to the shooter's right and negative to the shooter's left.
Maximum Point Blank Range
Maximum range for which the bullet does not go above or below the maximum point blank range radius.
Maximum Point Blank Range Zero
Zero range to achieve the maximum point blank range.
Range
Distance from the shooter along the line of sight.
Range at Max. Height
This is the range at which the bullet reaches its maximum height in the vital zone when doing the maximum point blank range calculation. This is NOT the maximum height of the bullet for the trajectory calculation.
Sectional Density
Bullet sectional density
Speed of Sound
The calculated speed of sound.
Stability
An approximated value of the bullet stability at the muzzle. This value should be greater than 1.5 (Don Miller says value should be 1.3 to 2.0). Values less than 1.0 are dynamically unstable and will tumble.
Time
The time of flight of bullet in seconds.
Velocity
The speed of the bullet in feet per second.
Windage
The distance to the right or left of the line of sight. Windage is positive to the shooters right and negative to the shooters left.