CRUSHER-GAUGE, an instrument for the indirect meas urement of the pressure in a gun when fired. Lead is the register ing agent for shotguns, but copper is used in other insthnces. The original type was screwed into the wall of a gun, and the explosion drove a knife-edged piston into a copper disk, the power required to penetrate to various depths being read off from a table. The modern form of gauge is a copper cylinder, compressed between two flat surfaces. Tables are prepared, for various crushers of standard length and diameter, from which the force in tons per square inch can be ascertained easily. Several crushers are tried in turn to give an average. The copper is first given an initial com pression in manufacture, a record of the results being made. The simpler method of placing is in the chamber at the back of the charge. A rifle gauge is illustrated in the drawing, before and after firing. It consists of a massive steel block into which a rifle-barrel is locked by means of a screwed gland-fitting. The cartridge base rests on a piston through which the firing pin (striker pin) passes. As the piston is driven back by the explosion it compresses the copper crusher lying behind the piston.
