What bullet is able to go through body armor?

Any cartridge could potentially go through body armour. There are several categories of body armour, each geared to a specific type of threat. The body armour which is meant to be worn under clothing without looking conspicuous is typically only capable of stopping pistol rounds fired through pistol length barrels, and can often be easily defeated by the same cartridges fired through rifle length barrels and rifle cartridges. Soft body armour has this limitation. The classes of hard body armour are rated to be able to stop up to a .30-06 or comparable cartridge.

Dedicated armour piercing rounds are designed and made from materials which will prevent their expansion after impact.