riflecaliber

Rifle caliber refers to the internal bore diameter of a rifle’s barrel and, by extension, to the cartridges designed to chamber and fire that bore. The term is used both as a measurement in inches (caliber .30, .22, etc.) and in millimeters (7.62 mm, 6.5 mm). In practice, caliber commonly denotes bullet diameter, and the cartridge used with that bore is often named to reflect it. However, caliber is not a direct measure of the firearm’s power, length, or weight; two rifles with the same bore diameter can fire cartridges that differ widely in case length, powder charge, and muzzle velocity.

Bullet diameter is usually close to the groove diameter; many rifles labeled as “.30 caliber” actually use bullets around .308 inches in diameter, while some older or specialty cartridges use .311–.319 inch bullets. Cylindrical cases and rim or rimless designs vary and affect chamber geometry and pressure. Cartridges are often described by a caliber name plus a case length or standard (for example, 7.62x39 mm or .223 Remington). The same bullet diameter can exist in multiple cartridge families, and conversely, cartridges of the same name may use different powders or lengths in different regions (for instance, 7.62x51 mm NATO and .308 Winchester are not identical, though closely related).

Common rifle calibers range from small game and varmint loads such as .22-250 and .223 Remington to large game and long-range rounds such as .300 Winchester Magnum and .338 Lapua Magnum. Caliber choice affects recoil, trajectory, terminal performance, and firearm compatibility.