Caliber is used to describe the size of a bore and the size of the cartridges designed for different bores

• Usually measured as the diameter of the bore from land to opposite land
• Expressed in hundredths of an inch, thousandths of an inch, or millimeters
• In some cases, the caliber is given as the diameter of the bullet, which is the distance between the grooves.
• Every firearm is designed for a specific Caliber