[@Absolis]
Bits of apocalypse skin are ridiculously tough, but soft. As such they make shit projectiles. The old 'indestructibilium can only be pierced by itself' rule doesn't apply when the material is soft. If you were able to get some Apocalypse bone, sure, but keep into account that Apocalypse's bones are able to withstand more than 100x as much force as his flesh. And his flesh can stop tank cannons with ease.