The caliber should be clearly printed on the barrel of the weapon. If unsure, consult a gun smith.
Only buy ammunition that matches what is printed on your barrel. There are a few exceptions but that is the general rule.
If it shoots accurately out of your firearm, any ammunition will make a clean kill if YOU make sure it goes into the right place.
We are not sure what you mean by "cleanest." All modern smokeless ammunition is adequately clean, in terms of firearm maintenance.
"The proper and safest way to clean and store a firearm is to first make sure that there is no ammunition in any part of the firearm. Take it to a gun smith to have it properly cleaned and when you pick it up, they can sell you a trigger lock for your gun. Always store your gun in a lock box."
You make sure the firearm is loaded with ammunition, and the safety is off (if there is one), and you aim down the sights. Then pull the trigger.
Open the bolt, inspect the magazine and chamber.
Open the bolt, visually inspect chamber for presence of cartridges.
Make sure the safety is on and visually check to make sure that the firearm is unloaded always keep the chamber open and never look down the barrell
Enter shooting and hunting tournaments. Make sure that you have the correct license, ammunition and rifle or shotgun for the competition.
Open the bolt, visually inspect chamber for presence of cartridges.
There are a few different thing to make sure an application is right. Always make sure what you writ down is true.
I usually doublecheck my work, just to make sure that it is correct. Let's make sure that we are on the right path.