Getting 3D Model Thickness for gun penetration simulations

Hi I plan to make a realistic gun penetration simulation and would need to determine 3D model thickness (including the thickness of its internal parts and gaps between them factored in), Please suggest the topics of this course that I should focus on primarily? And please include their prerequisite topics as well as my Math is not really as solid as yours, though I did manage to port a subset of OpenGL into a palm pilot more than a decade ago for an embedded project I was working on back then, but that only required the most basic 3D Engine concepts in Math turned into code and had OpenGLs code to start with. I hope you and this course could help me. Thanks