the 12 caliber." The 16th caliber is known as "lordly" . While shotgun bores can be expressed in calibers (the .410 bore shotgun is measured as .410 in in diameter, unlike with rifles the actual bore diameter of a smoothbore shotgun varies significantly down the length of the barrel, with the use of chokes and back-boring.

In the United Kingdom, "gauge" is referred to as "bore" and in the United States "bore" is referred to as "gauge", e.g. a "12-bore shotgun