Though they are a great choice for practice, especially on steel targets, most frangible bullets are a poor choice for personal protection because they act like solids when they hit tissue. The result is poor energy transfer and reduced tissue damage.
However, International Cartridge Corporation makes a line of ammunition with sintered, frangible bullets specifically designed for self-defense and law enforcement applications. The hollow-point bullet used in the company's Green Elite HP Duty loads is engineered so the nose will break into pieces in tissue, causing secondary damage, while the base stays intact to continue penetrating. But, if the bullet strikes a hard object, it disintegrates into powder. The ammo is being used by several police forces around the country as a safe but effective alternative to conventional lead-core, jacketed pistol ammunition.
Dan Smith of ICC makes a good point when he says, "Every time you pull the trigger, you own that bullet." Green Elite HP Duty reduces the chance of a bystander being hit by an over-penetrating bullet or ricochet.