Inspection of Cannon, Instruments for

These are used to verify the dimensions of cannon, and to detect the presence and measure the size of cavities in the metal. The star-gauge is an instrument for measuring the diameter of the bore at any point. The cylinder-staff is used to measure the length of the bore. It is supported by a rest of a T-form at the muzzle, and the extremity inserted in the gun is armed with a measuring-point and a guide-plate . The cylinder-gauge is a cylinder of cast iron, turned to the exact or true diameter of the bore. When used it is attached to the end of the cylinder-staff. The searcher consists of four flat springs turned up at the end, and attached to a socket which is screwed on to the end of the cylinder-staff. It is used to feel for cavities in the surface of the bore. The trunnion-gauge verifies the diameters of the trunnions and rimbases. The trunnion-square is used to verify the position of the trunnions with regard to the bore. The trunnion-rule measures the distance of the trunnions from the rear of the base-ring. Calipers , for measuring exterior diameters. A standard-rule , for verifying other instruments. The vent-gauges are two pointed pieces of steel wire, 0.005 inch greater and le than the true diameter of the vent, to verify its size. The vent-searcher is a hooked wire, used to detect cavities in the vent. A rammer-head , shaped to the form of the bottom of the bore, and furnished with a staff, is used to ascertain the interior position of the vent. A wooden rule , to measure exterior lengths. A mirror , a wax taper , beeswax ; rammer , sponge , and priming-wire . Figure and letter-stamps , to affix the required marks. The objects of inspecting cannon are to verify their dimensions, particularly those which affect the accuracy of the fire, and the relation of the piece to its carriage, and to detect any defects of metal and workmanship that would be likely to impair their strength and endurance.