Caliber - unit of measure indicating the interior, or bore, diameter of a firearm barrel and the diameter of the ammunition. It is measured in inches or millimeters.
For example, a .270 caliber rifle bore measures 270/1000ths of an inch in diameter.
Every rifle is designed for a specific cartridge. The ammunition used must match the barrel stamp on the firearm. If you cannot find the caliber stamped on the firearm, take it to a gunsmith
For example, there are several .30 caliber firearms that use the same bullet size but are designed for different cartridges. These include the .30-30, 30-06, .308, .300 Win Mag, etc.
