Tools used in the PROOF of Cannon, are as follows:
Searcher, an iron socket with branches, from 4 to 8 in number, bending outwards a little, with small points at their ends: to this socket is fixed a wooden handle, from 8 to 12 feet long, and 1½ inch in diameter. This searcher is introduced into the gun after each firing, and turned gently round to discover the cavities within: if any are found, they are marked on the outside with chalk; and then the
Searcher with one point is introduced: about which point a mixture of wax and tallow is put, to take the impression of the holes; and if any are found of one-fourth of an inch deep, or of any considerable length, the gun is rejected as unserviceable to the government.
Reliever, is an iron ring fixed to a handle, by means of a socket, so as to be at right angles; it serves to disengage the first searcher, when any of its points are retained in a hole, and cannot otherwise be got out. When guns are rejected by the proof-masters, they order them to be marked X thus, which the contractors generally alter WP thus; and after such alteration, dispose of them to foreign powers for Woolwich proof.
The most curious instrument for finding the principal defects in pieces of artillery, was lately invented by Lieutenant-general Desaguliers, of the royal regiment of artillery. This instrument, grounded on the truest mechanical principles, is no sooner introduced into the hollow cylinder of the gun, than it discovers its defects, and more particularly that of the piece not being truly bored; which is a very important one, and to which most of the disasters happening to pieces of artillery are in a great measure to be imputed; for, when a gun is not truly bored, the most expert artillerist will not be able to make a good shot.