Abstract: A shear gage for measuring the pressure reached in a firearm cartridge loed within the barrel when a high caliber gun is fired. The design of the shear gage involves the shearing of a uniformly distributed loaded circular plate at its circumferential support in the event that a predetermined maximum critical shear pressure is exceeded. Stresses due to bending and shear were analyzed to select the proper hole diameter to thickness ratio to ensure that the disc or plate fails due to a shearing failure and not a bending failure. A series of varying sized circumferential supports may also be positioned within the chamber to provide a range of critical failure pressures to more precisely estimate the actual pressure that occurs within the chamber or cartridge.