In using this sight, the thumb-screw is first loosened, and the rear end of the sight raised until the mark on the trunnion coincides with the degree of elevation required for the range, as given in the Tables: clamp the thumb-screw, and elevate the gun until the bubble is at 0°, then give the lateral training.
226. Tangent-sights placed on the side of the breech, with a fixed front sight on the rimbase, as in rifled cannon, will hereafter be supplied to all pivot-guns; and these will give the sight with equal accuracy at all elevations.
227. Rammer-heads are to be made of well-seasoned ash, birch, beech, or other tough wood, of the form and dimensions given in the drawings furnished by the Bureau to the different Navy Yards. The face of the rammer is hollowed, so as to embrace the front of the ball and press the selvagee wad home in its place. A hole is bored lengthwise through the head to admit the tenon, which is fastened by a pin of hard wood, three-tenths of an inch in diameter, passing transversely through the head and tenon. The diameter of the staff is 1.75, and that of the tenon 1.5 inch. The diameter of the rammer-head will be 0.25 inch less than that of the bore or chamber to which it is adapted.
For all chambered guns except those of the Dahlgren pattern, the rammers will be adapted to the chamber, but, as above described, will answer equally well for the shot and selvagee wad.
Staves are made of tough ash, and are one foot longer than the bores of the guns for which they are intended: they are to have grooves 1/16 of an inch deep and 1/4 of an inch broad cut in them to show when the "ordinary charges" are in place, and, by due allowances, the others also.
For rifled cannon, rammer-heads are made of composition, of the pattern prescribed by the Bureau.
228. Sponge-heads are to be made of poplar, or other suitable light wood. A hole 1.5 inch in diameter is bored through the axis to admit the tenon of the staff, into which the worm is previously secured by means of a brass pin which passes through an eye in its shank and the tenon. The worm is intended to project half an inch beyond the face of the sponge-head, when the tenon is in place, and to have free play back into its socket when pressed against the bottom of the bore. It must be two inches in length and one and a quarter inch in diameter, made of elastic brass or composition wire two-tenths of an inch in diameter, and tapering at the points, so as to preserve its elasticity and firmness. It is to be left-handed, in order to act when turned to the right, or with the sun.
The wood of which sponge-heads are made should be well seasoned, and gotten out of a size but little greater than the diameter of the heads for which it is intended, so that there may be as little shrinkage as possible in the finished heads.
The heads, when finished, should also be primed with several coats of boiled linseed oil or varnish, as the porous wood of which they are made is apt to become water-soaked, or to split on exposure to the air.