"Armour Piercing", Arifureta Vol 12

“Oh, I just made some armor-piercing bullets to deal with you guys," Hajime replied casually.
Traditional armor-piercing bullets were made by putting a hard metal core Jat the center of the bullet to increase its penetrating capacity. Hajime had used ultra-compressed, ultra-dense azantium for his bullets' cores. He'd also enchanted the softer outer layer with a spatial barrier.
Against most living creatures, the bullets' penetrative power was actually so high that they didn't cause much damage on their way through something, but they were perfect for destroying an apostle's core.