Those articles are done by Nathan Okun. I won't be quite wrong if I say that he is the most expert man in the world today regarding questions of gun versus armor interaction. I know he was done some very accurate and user friendly DOS programs, the most important of them called "facehard" that, with input of the shell qualities, Armor scheme and quality, the speed and angle of impact, etc, will do a calculation of how ill the shell be interacting with the armor, if the shell will be decapped, stopped, or will penetrate the armor.
I will look where to download it and will post a link, it is a little program for free AFAIK. I myself did some "experiments"

and the program is a beauty.