Caliber refers to the diameter of the bullet and the diameter of a firearm's barrel. Even within a single caliber, there are several variations: .38 special is different ammunition than .380 ACP (9mm short) which is different than .38 Long Colt, which is different than .38 Short Colt which is different than .357 Magnum, which is different than 9mm parabellum. These differences have to do with the size & shape of the cartridge (brass) and how the firearm is designed to shoot it. All of those calibers mentioned above are roughly the same diameter though.
A type of ammunition.
air rifle
.30 caliber.
No
DO NOT DO THIS!!!!!!!!!!!!!!!!!!!!
.357
No
Could you be a little more specific? There are lots of rifles considered large caliber, therefore there are all sorts of ammunition.
It denotes a type of 30 caliber ammunition adopted by the Military in 1906.
The 7.62x59 ammunition is a surplus ammunition used in the Mosin Nagant
It is marked on the barrel.
No one that I am aware of.