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Course Outline

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

  • Caliber usually is measured as the diameter of the bore from land to opposite land and is expressed in hundredths of an inch, thousandths of an inch, or millimeters. For example, a .357-caliber handgun bore measures 357/1000ths of an inch in diameter between the lands and has a larger bore diameter than a .30-caliber handgun. However, there is no standard established for designating caliber. In some cases, the caliber is given as the diameter of the bullet, which is the distance between the grooves.
  • Every handgun is designed for a specific cartridge. The ammunition must match the data stamp on the firearm. If you cannot find the caliber stamped on the handgun, take it to a qualified gunsmith.
Handgun calibers

The circles show bore sizes of common calibers. Having the same bore size does not mean different cartridges are interchangeable.

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