Topic summary
4.5 mm caliber
Extracted from the Wikipedia article .177 caliber.
The .177 caliber or 4.5 mm caliber is the smallest diameter of pellets and BB shots widely used in air guns, and is the only caliber generally accepted for formal target competition. It is also sometimes used for hunting small game, like fowl. It is also used in field target competitions, where it competes with .20 caliber (5 mm) and .22 caliber (5.6 mm) rifles.