20mm×125mm

20mm×125mm refers to a specific cartridge dimension, indicating a projectile with a diameter of 20 millimeters and a case length of 125 millimeters. This nomenclature is commonly used in firearms and ammunition contexts to describe the physical characteristics of a round. The first number, 20mm, denotes the caliber, which is the internal diameter of the gun barrel and the approximate diameter of the projectile itself. The second number, 125mm, specifies the length of the cartridge case, the cylindrical container that holds the propellant and the projectile.

While this specific combination of 20mm diameter and 125mm case length might not correspond to a widely recognized or standardized military or commercial cartridge, such dimensions are typical for certain types of automatic cannons or specialized ammunition. The 20mm caliber is often found in anti-material rifles, autocannons for aircraft, or naval guns. The case length significantly influences the amount of propellant that can be loaded, which in turn affects the muzzle velocity and the overall performance of the cartridge, including its range and penetrating power. Ammunition dimensions are critical for ensuring proper function within a firearm's chamber and action, and precise measurements are essential for safe and effective operation. Variations in case length, even by a few millimeters, can render a cartridge incompatible with a specific weapon system.