20 mm caliber Wikipedia
20 mm caliber is a specific size of popular autocannon ammunition. It is typically used to distinguish smallercaliber weapons, commonly called "guns", from largercaliber "cannons" ( machine gun vs. autocannon).All 20 mm cartridges have an outside projectile diameter and barrel bore diameter of inches ( mm). These projectiles are typically 75 to 127 mm (35 in) long, cartridge ...