Drag Table File Format
When the program is started it looks for up to twenty files in its current directory (usually c:\bexw) that have the extension DCT (Drag Coefficient Table). These files can then be selected from the Trace window by clicking the drag table select button.
The drag tables are just ASCII text files. Each line of the file must end with a return. The first two lines are used only to identify ownership and the source of the table. These lines are not used by the program, but something must exist on these two lines.
The third line is the name of the function, such as G1, and can be from one to eight characters in length. A description of from one to forty characters follows the name, but the name must be separated from the description by a single comma. The function's name should be used for the file's name (G1 function becomes the G1.DCT file).
The fourth line through the last line of the file contain the deceleration data. The first number on each line is a velocity and the second number is the drag coefficient for that velocity. The first and second numbers must be separated by a single comma.
The first number on the fourth line is the lowest velocity for the table and the first number of the last line is the highest velocity for the table. The increment between velocities can be anything from 10 f/s to 200 f/s, but the same increment must be used for the whole table.
The lowest velocity for the table must be a multiple of the increment between velocities. For example, if the increment between velocities is 50 f/s, the lowest velocity for the table could be 50, 100, 150, 200, etc. However, it couldn't be a value such as 25, 75, 115, or 175 because these values can't be evenly divided by 50.
The drag coefficient is the deceleration of the bullet in feet per second per second for the corresponding velocity divided by that velocity. For example, if a bullet decelerates at 68.19 f/s² when its velocity is 1000 f/s (assuming standard speed of sound), then it's drag coefficient is 0.06819 (68.19 ÷ 1000). SAAMI tables use a different method to linearize the drag coefficient, and thus, they can't be used directly with Ballistic Explorer. Note that SAAMI drag tables, and thus, our tables are calibrated for standard Metro conditions.
Part of the G1.DCT file is listed below. While the specific values within the table are copyrighted, we are dedicating the file format to the public domain.