Ja, III is hard armor for rifle threats, IV is hard armour for defeating AP threats. The levels are simply the USA NIJ ones, Europeans use a different standard. Nevertheless level IV doesn't have to be a plate, it can be any form as long as it meets the requisites laid out in the lates (2004) nij standards. One new vest has hundreds of little titanium-ceramic coins all over it, dragonscale or something.
Werewolf, yea maybe ittybitty is bad word, but when you see the silver-dollar hole in an M1A1 hit by a Maverick missile it just seems small!
Rich, yea Uranium combusts when in the presence of oxygen, which is a bonus, and the shearing is nice. However Europeans aren't lazy and they have new tungsten penetrators that shear in a similar manner. Before the tungsten rod would sort of mushroom at the tip. Anyway I think that all penetrators, not just DU ones, 'bite' into sloped armor. It has nothing to do with shear, that would counter the effect, what happens is that the rods aren't actually pointy, that's just a windcap on them. They're blunt at the front, so the windcap falls away and this blunt rod can dig into very sloped armor.