Comment by shadowgovt

The challenge of classified info is that you don't know what knowledge a potential attacker has. This is why so many things that seem either obvious or irrelevant can end up on the classified list.

Sure, details on the tungsten penetrator by themselves may be either semi-obvious or worthless (wow, it's a round that penetrates things. Shocking a tank would carry such a weapon!). But the Chinese don't know if their potential opponents in the field know something about, say, the quality of tungsten China industry can access, or if they could extrapolate something about the operation of the main gun itself from the reported penetration numbers on the tungsten round.

This is why classification tends to be a wider net than seems necessary.