Ok, so then the real thing I'm learning here is that the shell is made out of the lighter, softer material to deliver the energy. They put the penetrator cap on, usually made of steel or some stronger heavier material, but it's thin so not significantly decreasing shell velocity. However, the shape of the penetrator allows for the energy to be delivered all at one precise spot, but it causes the flight characteristics to suck. To get the flight back, they add a thin lightweight material back over the penetrator that is negligible in terms of reducing the energy the penetrator delivers.

Cool

[–] setsneedtofeed@lemmy.world 2 points 18 hours ago* (last edited 18 hours ago)

Almost.

The cap (the "penetrative cap" as the above picture calls it) protects the hardened tip of the shell itself, so that the tip doesn't deform immediately on impact with armor. Soft metal caps did exist and work, but hard metal caps became more common since the hard cap would survive a little bit longer and thus get the shell better positioned to penetrate by the cap hopefully going through the outer layer of armor before the tip on the shell came forward to penetrate the remaining armor.