At the velocities and energies of armor-piercing projectiles impacting their targets, everything behaves more or less like a liquid, as can be seen here. You'd think it's like metal-against-metal, but it's more like shooting a small birthday cake into a big one.
Bandkanon 1 (Bkan 1) - self-propelled artillery with auto-loader. The big box seen here is the magazine that enabled it to fire 14 shells in 45 seconds from its 155 mm cannon.