Caliber, gauge, and the Data Stamp
Only one size of ammunition properly fits any firearm. Putting any other size cartridge into a firearm is extremely dangerous. The best way to make sure you are putting the correct ammunition into your firearm is to match the data stamp on the barrel of your firearm to the similar data stamp on the case of the rifle cartridge or shotshell. Be particularly careful with hand-loaded ammunition as it could be mis-marked.
Caliber and gauge
Ammunition comes in different lengths, shapes, and diameters depending on the type of bullet or case used. You must choose a caliber or gauge that is suited to your firearm as well as the game you wish to hunt.
The data stamp
First, you must know the caliber or gauge of the firearm for which you are buying ammunition. To find that out, locate the data stamp on the barrel of your firearm. Does the data stamp on the ammunition match the data stamp on the barrel? If you are not sure always get help from a knowledgeable person. It is easy to be confused by all the different ammunition. Ask someone who is experienced and is familiar with your firearm to help you select the correct ammunition.