287. "Elevate or Depress as directed!" If the carriage is fitted with a quoin, handspikemen standing between the handspikes and the side of the ship, place their handspikes on the steps of the carriage and raise the breech. As soon as the quoin is free, the 2d Captain takes hold of it with both hands and withdraws the quoin to the full extent; handspikemen "raise" or "lower" the gun slowly and steadily. When the proper elevation is given, the Gun Captain gives the word "Well!" and the 2d Captain forces the quoin tight under the breech, giving the word "Down!"
288. To facilitate the operation of pointing guns according to the distance of the object aimed at, sights are prepared and fitted to each gun; and breast-sweeps for all truck-carriages of heavy guns.
The ordinary sights consist of two pieces of bronze gun-metal, one of which, called the reinforce-sight, is a fixed point, firmly secured to the sight-mass, upon the upper surface of the gun between the trunnions. The heads of the sights should not be bright, otherwise it interferes with the aim when they are exposed to a bright sun.
289. The other, or breech-sight, is a square bar or stem, with a head, in the top of which is a sight-notch. It is set diagonally, so as to expose two faces to the rear; the rear angle chamfered, to afford a bearing for the clamp-screw. This bar or stem is made to slide in a vertical plane, in the sight-box fixed to the breech sight-mass, and is held at the various elevations for which it is graduated by means of a thumb-screw. Its length is sufficient for all the elevation which can be given—about 5°—before the muzzle appears above the front sight, after which a long wooden sight must be used, graduated for the whole length of the gun, using the notch in the muzzle.
The bar or stem of the sight has lines across its faces denoting for all the old guns degrees of elevation, each of which is marked with the number of yards at which a shot or shell will strike the point aimed at, when that line is brought to a level with the top of the sight-box, and the gun is loaded with a specified charge of powder; for the guns of the new system, the ranges are marked in even hundreds of yards.
The uppermost line on the stem marked level is the zero of the other graduations, and when adjusted to the level of the top of the sight-box, the bottom of the notch in the head of the breech-sight and the apex of the reinforce-sight show the dispart of the gun. When the line of sight coincides with these points, it is parallel to the bore, and when continued to a distant horizon, the gun is laid level or horizontal.
Sights should invariably be made so that the level line on the stem will correspond with the bottom of the head when it rests on the sight-box, and thus secure a dispart-sight in case of accident to the screw in the sight-box.
A white line, one-fourth (.25) of an inch wide, drawn on top of the gun from the breech-sight to the notch on the swell of the muzzle, has been found to greatly facilitate the aim. For night-firing a broad wooden block, painted dead-white, to ship over the reinforce-sight, leaving 1/4 of an inch of the sight exposed, will assist in preventing the aim from being too high.
290. For shot-guns the ranges in yards for one shot with the distant-firing charge of powder are marked for each degree of elevation on the right in-board face of the sight-bar; for the ordinary firing, on the left face.
291. The gun being placed a certain height above the water, depending on the class of vessel and the deck on which it is mounted, it is evident that, when the axis of the bore is horizontal, the shot will have a range proportionate to this height. This range or distance is commonly called point-blank, or point-blank range, and is the number noted in the column marked P.B., or 0°, or level in range tables.