Input Requirements

The program will first ask you to enter a variety of parameters. The parameters are as follows:

caliber-the diameter of the bullet in inches or millimeters

bullet weight-measured in grains (7000 gr/lb) or grams

muzzle velocity-measured in feet per second or meters per second

far-zero distance-the range at which the rifle is zeroed

sight height-the height of the sights above the barrel

point blank diameter-the diameter of the "must hit" zone of the target

altitude-height above sea level, measured in feet or meters

temperature-measured in degrees Fahrenheit or Celsius

wind speed-measured in miles per hour or kilometers per hour

wind direction-from 0 to 12 o'clock, fractional hours okay

trajectory interval-measured in yards or meters

ballistic coefficient / bullet shape class-a measure of the aerodynamic efficiency of the bullet

The first five parameters are required, as is the ballistic coefficient or bullet shape class. The remaining parameters can be left at their default settings, if you wish. Pay particular attention to the "trajectory interval" parameter. The units of the output table, notes, and graph are determined by the units you choose for the trajectory interval. If you select "yards", the output will be in English units. If you select "meters", the output will be metric. The maximum range of the plotted trajectory will always be ten times the trajectory interval.

Description of the Output

The input parameters are listed at the top of the page so they will be handy if you print it out. If you specified a shape class rather than a ballistic coefficient, the software will show you the ballistic coefficient it calculated based on the shape, size, and weight of the bullet. Next, the trajectory is presented in tabular format.

The trajectory table shows bullet velocity, kinetic energy, time of flight, wind deflection, true drop, and drop from line of sight at 10 intervals of the distance and units you've chosen. The sign convention for wind deflection and apparent drop uses negative numbers when the bullet is to the left of or below the line of sight and positive numbers to the right or above. Since true drop is always negative according to the convention, its sign is implicit. Wind is always described as coming from a particular direction. Using the clock face, 12 o'clock (or 0) is from straight ahead, 3 o'clock is from the right, 6 o'clock is from the rear, and 9 o'clock is from the left. You are free to specify any hour and/or fraction thereof between 0 and 12. The components of the cross-wind across and along the trajectory are calculated and accounted for.

The trajectory notes show the near-zero, maximum bullet height above line of sight, and the point blank range for the chosen diameter.

The apparent drop and kinetic energy are graphed in detail. The apparent drop curve is shown in black and uses the scale on the left while the kinetic energy curve is shown in dark gray and uses the scale on the right side of the graph. The line of zero apparent drop is shown on the graph, as is a light gray bar that shows the point blank diameter.

The formulas used and calculations performed by the Web Ballistics Computer are believed to be accurate. However, the accuracy of the data is unwarranted.

Running the Program

To run the program, just click here.

Acknowledgements

The Web Ballistic Computer is original software based in part on the equations derived by Arthur J. Pejsa and published in his book, Modern Practical Ballistics (ISBN 0-96212776-3-7). It is available from:

Kenwood Publishing
2120 Kenwood Parkway
Minneapolis, Minnesota 55405.

The graphical output is made possible by the GD Library, available from http://www.libdg.org.

Revision History

The current version (as of 9/10/97, 7:30 PM PDT) is 2.2. Revised intro. Added a horizontal line in the trajectory graph to clearly indicate zero apparent drop. Also added a faint gray bar to indicate the flight of the projectile through the point blank diameter.

Version 2.1. Fixed a nasty bug that resulted in server errors when plotting the graphical trajectory with metric input parameters. The bug was camouflaged by an unrelated problem with the University's web servers that also resulted in server errors. Both problems have now been fixed. If you used metric parameters with version 2.0, the trajectory table was reliable but the graphical output, if any, could be bogus. I recommend that you re-run your parameters with this version to produce an accurate trajectory graph.

Version 2.0. Added graphical output for apparent drop and kinetic energy. Reformatted the output page again to accommodate all the necessary information, including the graph, on a single printed page.

Version 1.3. Changed the parameter summary on the output page to a more compact form so the results would fit on a single printed page. Improved the error handling so each out-of-range parameters is noted rather than simply announcing an error and reprinting all parameters. Added a temperature-compensated calculation of the speed of sound and the range at which the projectile is transonic, if any.

Version 1.2. Added flexible trajectory intervals for the output table. To save screen real estate, I changed this Intro page so that it is overwritten by the Parameter Input page rather than opening a new window.

Version 1.1. Added cross-wind speed and direction calculations. Modified HTML to produce a white background for all pages and to open separate WBC input and output windows.

Version 1.02. Fixed non-standard HTML in the input and output tables as well as a bug that increased the apparent drag on bullets with low ballistic coefficients and high velocities.

Version 1.01. Fixed a bug that froze the muzzle velocity at 2700 fps and the sight height at 1.5 inches.

Version 1.00. Went public on 11/29/96.