Compatible with all 4.5mm PISTOLS / hand guns used for self defense purposes usually comes in pack of 1500’s. A steel BBS is a type of 4.5mm round bullet used for engagement in self defense purposes. There are many types of 4.5mm pistol that can be used for self defense. It can also be used for training purposes. It is a light metal material, which is also why it is known to be one of the faster types of bullet (in speed) and it can also be used on short to medium range.