Chamber pressure

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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 (MPa), while the American SAAMI uses the pound per square inch (psi, symbol lbf/in²) and the European CIP uses bar (1 bar is equal to 0.1 MPa).

Regardless of pressure unit used, the measuring procedure varies between CIP method, SAAMI method, and NATO EPVAT.^{[clarification needed]} 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 (which for example can be denoted psi CUP, bar CUP, or MPa CUP) or lead units of pressure (LUP).^{[citation needed]}