Bullets come in different shapes and sizes and are commonly made of lead and copper.
In addition to the caliber of your ammunition, you must also decide on weight. The weight of a bullet is expressed in grains. Generally, the heavier the bullet the more power it delivers.
Modern bullets are designed for particular sizes of game animals. It is possible, for example, to choose a bullet weight that is too light for large game. If the weight is incorrect you may end up wounding the animal rather than killing it quickly.