The Powley "Secant Flat Base" projectile is the same as the Aberdeen Proving Ground G8 projectile.
Some custom bullet makers like JLK bullets produce "VLD" flat based bullets for bench rest shooting. This standard projectile would be suitable to model the external ballistics of such bullets.
The program uses second order polynomial drag functions, which were fitted to the drag table data, to calculate the drag for a given velocity. Those functions are as follows: