Bullet designs vary widely, not only according to the particular firearm used (e.g. a 9x19mm Parabellum caliber hollowpoint handgun cartridge will have inferior penetration power compared to a 7.62x39mm rifle cartridge), but also within individual cartridge designs. As a result, whilst so-called "bullet-proof" panels may successfully prevent penetration by standard 7.62x39mm bullets containing lead cores, the same panels may easily be defeated by 7.62 x 39 mm armor piercing bullets containing hardened steel penetrators.