What is Chamber pressure?

Within firearms, chamber pressure is the pressure exerted by a cartridge case's outside walls on the inside of a firearm's chamber when the cartridge is fired. The SI unit for chamber pressure is the megapascal , while the American SAAMI uses pounds per square inch and the European CIP uses bar.

Regardless of pressure unit used, the measuring procedure varies between CIP method, SAAMI method, and NATO EPVAT. The chamber pressures are measured to different standards thus can not be directly compared. Chamber pressures have also historically been recorded in copper units of pressure or lead units of pressure.