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.
Changing the weight of your bullet changes its trajectory. Trajectory is the path a bullet takes during flight. Several factors affect this path: gravity, air resistance, speed and weight of the bullet. Gravity pulls the bullet down as it travels forward which results in a downward curved flight path. The air provides resistance that slows the flight of the bullet.
Of course, a bullet travels much too quickly for you to be able to actually see its trajectory. You can see an example of a trajectory though by simply throwing a ball in the air and watching it come down.
The trajectory of a bullet is slightly curved. So, if you sight in your firearm to hit a target at 200 yards, you will hit your target high at 100 yards and low at 300 yards.
Since the trajectory of a bullet depends in part on its weight, you must carefully consider your weight choice. For example, a .30-06 Springfield cartridge with a 180-grain bullet has a different flight pattern than the same cartridge with a 150-grain bullet. Once you make your selection, practice sighting in your rifle using that ammunition before you head into the field.