ZZDrag

The zzDrag app computes ballistic coefficients for multiple drag models by entering critical bullet dimensions measured with a micrometer or obtained from the manufacturer. The most appropriate drag model for the bullet is determined by comparing the ballistic coefficient values over a range of input bullet velocities. The drag model which produces the lowest standard deviation for the computed ballistic coefficient is the model which will most accurately predict bullet flight trajectory.

The following drag models are used by zzDrag in the comparison described above:
G1 drag model - the standard drag model for bullets with a flat base and 2 caliber ogive.
G5 drag model - created for moderate (low base) boat tailed bullets with a 6 caliber tangent nose design.
G6 drag model - created for flat based bullets with a 7 caliber secant nose design.
G7 drag model - created for "Very Low Drag" boat tail bullets with a 10 caliber tangent nose design.
G8 drag model - created for flat base bullets with a 10 caliber secant nose design.

The app will display the best (mean) ballistic coefficient to be used for the bullet based on the velocity range over which is it is to be used. This requires the muzzle velocity and a terminal velocity. For example, if the bullet is to used for 1000 yard target shooting, the velocity at 1000 yards would be used as the terminal velocity. If, on the other hand, it is to be used for hunting deer sized game, the velocity at which the bullet falls below 1000 ft-lbs of energy may be a good choice for the terminal velocity.

The zzDrag app computes the amount of drag contributed by the bullets nose, skin, base, and boat-tail for any of the supported drag models over a range of velocity values. The core algorithms are those developed by Robert McCoy in his McDrag Basic program.

The bullet properties entered once are saved in an internal database for later recall. The bullet dimensions can be entered in inches, millimeters, or calibers.

Bullet stability is computed by zzDrag using the barrel twist rate, bullet properties including plastic tip length and environmental factors if desired. The environmental model used is the ICAO. The standard atmosphere can be used to compute pressure and temperature from elevation, or they can be entered directly in either English or metric units. Bullet stability is shown as the "s" output in the algorithms developed by Michael Courtney and Donald Miller in their paper "A Stability Formula for Plastic Tipped Bullets". S values less than 1 are shown in red as unstable. The "s" value cutoff value for stable is select-able as either 1.3 (bench rest), 1.5 (military), or 2.0 (extreme weather).

All reports can be written as either a csv (comma spaced values) file for import into a spreadsheet program or saved as a PDF (Portable Document File) for viewing on multiple hand-held or computer platforms.