The GMDR.Load External Ballistics Calculator

For that very small and select community interested strictly in internal ballistics, what happens to the bullet after leaving the gun's muzzle, is of little interest. For the rest of us, hunters, paper punchers or plinkers, the trajectory of that bullet is of vital interest - it's what "gunning" is all about. GMDR.Load provides one of the industry's most complete and accurate external ballistics calculator (XBC).

The XBC GMDR.Load presents to the user is highly graphical and interactive: one where once the user has selected a bullet or factory load for which the trajectory is to be computed, the trajectory will be continually updated as long as the user changes the conditions of that calculation. When the trajectory is redrawn, the user is given both a lateral and axial view.


 External Ballistic Calculator screen dump


The parameters which the XBC allows the user to modify are: target distance; "zero" distance; target diameter; inclination; sight height; sight-in distance; sight-in vertical offset; gun rotation (cant); ambient temperature; relative humidity; altitude; pressure; winds, head/tail and cross; and the muzzle velocity.

The user also has control over: the distance units used - yards, meters or feet; the presence or absence of subwindows presented by the XBC: drop as expressed as MOA, MILs or "Clicks"; trajectory specifics, a tabular form of the trajectory; and the type of "zero" used during trajectory calculations. "Local", "standard" or "Special" zero options are available to make simple and fast the transition from the range where the gun was zeroed to the field conditions.

GMDR.Load features a catalogue of more than 1100 standard bullets with their Ballistics Coefficients and a catalogue of more than 900 standard factory loads. Both are accessible through a drop down menu. The user can add new bullets to the catalog.

Once a trajectory has been calculated, the user can inquire of the specifics of that trajectory by simply clicking on the trace - information about that subset of the trajectory will be displayed (in a small window).


 Trajectory Specifics window

Once a trajectory has been calculated, the user has the option of retaining it for later comparisons (up to 5 reference trajectories). GMDR.Load has the ability to optimize the Point Blank Range of a trajectory, given a user dialable target diameter.

Because GMDR.Load calculates all trajectories based on the underlying equations of motion (first principles, real physics), instead of table lookups, no corrections are necessary for uphill, downhill, head/tail or cross wind, or canted shooting. The user can set the quantities to be displayed in either SAE or Metric units. Detailed tables with the projectile's drop, horizontal displacement, remaining velocity, energy and time of flight at different intermediate range positions can be displayed on the screen simultaneously with the graph. All screen displays are point and click printable