All of this "guess-work" and reliance on the math involved in KE, SD, etc. (I am not picking on anyone here- just a general observation
) makes me wonder why folks don't just use the Schwartz or MacPherson bullet penetration model (of both) and be done with it.
Either model will predict with a reasonable degree of precision and accuracy (+/- 1 cm), the penetration depth of a non-expanding projectile (Heck, you don't even have to do a test for non-expanding stuff like FMJs, HCSWCs, etc.) in calibrated ordnance gelatin or soft tissue.