There could be different ballistics vests implemented with specific armor levels. (Type I, Type IIA, Type II, Type IIIA, Type III, Type IV) Depending on the level, the could take a few rounds of the round they were designed to stop. This would force bandits that might want that body armor to aim for the head or limbs. Also, with the helmet, it can stop a round or two from a handgun and a very small chance that it can stop a rifle round, since it has happened before. In reality, if you fire a round into a helmet, it might alter the course of the round and save your life.