239. All vessels carrying XI and IX inch guns, and all iron rifles, are to be furnished with an impression-taker and wax. Impressions of the vent and bore, as described in Art. 57, are to be taken after every ten shotted rounds in practice, and at the close of an action. The last one should be preserved for comparison with the succeeding one; and when, in the opinion of the Commanding Officer, the wear becomes excessive, or a decided crack shows itself, a duplicate must be forwarded to the Bureau for examination. In forwarding them, they should be tacked on a piece of thin board secured in the bottom of a box. If wrapped in cotton or oakum they are generally defaced. The date, number of fires, Register Nos. of guns, ship from which forwarded, and other remarks written and pasted on the under side of the box-cover.
In expert hands any small spar—such as a boat's mast—will take the impression equally well.
240. Passing-boxes are to be made of strong and well-tanned harness or sole leather, strongly sewed, or of such other material as may be directed.
For 8-inch and 32-pounder guns they are to be of sufficient height to contain two near-firing charges.
Their diameters, in the clear, must be half an inch greater than those of the cartridges they are to contain.
Their tops must be distinctly lettered, in letters one inch and a half long, with the calibre and class of gun they are intended to serve, and made to slide on the beckets.
241. All passing-boxes are to be painted black, with the calibre and charge painted in white letters two and one-half (2 1/2) inches long on the side, and one and one-half (1 1/2) on the top.
242. If, however, there are any guns of the same calibre on spar-decks requiring lighter charges, the lower half of the box shall be painted white.
For gun-decks in similar cases the lower half shall be painted red.