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Immediately after casting during cleaning up, a visual inspection of the exterior of the piece was made to detect any obvious surface flaws which exceeded accepted limits. After machining the interior of the bore was first examined for 'spongy' areas or cavities, a process known as searching, the implement used being called a searcher. It consisted of a wooden stave at one end of which were a number of wire points designed to catch in any cavity when moved around in the bore. The points could be retracted by a ring which slid up the stave. Another form of searcher was designed to take a wax impression of any cavity detected which, if 1/9 inch or more in depth caused the gun to be rejected. The earliest reference to the searcher occurred in 1635. Another test was to suspend the gun by the muzzle, fill the bore with water, and observe the outside of the piece for seepage indicating porosity of the metal. During the 18th century a more severe test was introduced by putting the water under high pressure, but was discontinued in 1780 as being unnecessary for bronze guns.
The bore was gauged for accuracy and straightness, tolerances being pretty liberal - at one time plus or minus 0.1 inch (2.5 mm) for calibre! Having passed the above tests the gun was then fired with charges well above the maximum service charge, often being double-shotted as well. There followed another visual inspection and examination after which the gun, if found serviceable, was passed to the engravers. A weakness in a bronze gun appearing after proof usually took the form of a bulge in the barrel, which of course meant rejection. Cast iron guns were not so considerate; they invariably burst during firing. Consequently Gunners of the smooth-bore era naturally preferred to serve on bronze guns rather than on iron! |
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WL Ruffell Issue 85 March 1995 |
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