Breeching Taps.—The usual diameters of rifle breech pins are three-eighths, one-half, and five-eighths of an inch; of shot guns three-quarters and seven-eighths of an inch. The thread of the rifle is generally fourteen to the inch, and the shot gun sixteen to the inch. The breech pins of military arms vary. Some are made with coarse thread and some with fine thread, ranging from ten to eighteen threads per inch. There is no arbitrary rule for breeching guns, and excepting English made guns, almost every conceivable size and thread may be found in guns that are brought in to be repaired. In rifle and shot guns the fourteen and sixteen thread will be found to predominate. In unbreeching guns that have been made by “experts” of some country town, who built the arms “to order,” or in overhauling guns that have been repaired at the same kind of establishments, it will not be uncommon to find threads in the barrels that have been cut with a blacksmith’s taper tap, and the pin tapered to suit the thread so formed. It will be nothing uncommon to find a breech that is made to one side of the bore, or made with a crooked thread. If tapped with the taper tap, the thread may be found to be ten or twelve to the inch, according as a tap to fit the breech could be found.
Let the workman discard all such ways of breeching guns. Let him procure a set of taps of the sizes and threads as noticed at the beginning of this article, and “stick to these sizes.” If the thread in a gun be worn, and the pin be loose or leak fire, then ream out the old thread, cut it anew, and put in a new pin.
Figure 36.
Breeching taps should be made in pairs, one tapered a little and its mate made straight and with a full thread, so as to cut full at the bottom where the thread terminates. If the first tap be not tapered a little, the thread should be nearly all removed at the end, and gradually increased for five or six threads, when it will be of full size. A stem or projection is made as shown in the cut, [Fig. 36], which enters and fills the bore of the gun and so serves to insure a thread straight with the barrel. If the bore be larger than the extension, slip over it a piece of brass tube or a ferrule of some kind, until it fits a little snug in the bore. If but little be wanting to make the fit, a piece of writing paper or a bit of card may be wrapped around it. Old-fashioned gunsmiths have been known to wind tow around an extension to make a fit.
Figure 37.
The diameter of these extensions must be that of the smallest bored gun in which they will be used. The extension of the shot-gun tap may be about half-inch diameter. The length of the extension may be about an inch for rifles and an inch and a quarter for shot guns, the thread about an inch in length. The whole length of rifle taps may be about three and a half inches, for shot-guns about four inches.
Breech Pin Formers.—These tools are made of steel and have holes drilled through them and cutting teeth formed on one end (as shown in [Fig. 37]). In use it may be held stationary, and the breech-pin turned in the hole until the teeth form it to size and remove enough in length for the screw to be cut on the pin. Eight teeth are enough for the smaller sizes of these tools. If made with more teeth they are consequently finer and shallower and do not operate so well, or cannot be ground to an edge or sharpened with an oil stone if they become dull. The sizes must correspond with the size of the breech taps, or a little less than this size, as the dies used in cutting generally “raise” a thread a little larger than the work. The length of these tools may be about three-fourths of an inch or an inch, as may be best to make them. In use they can be held in a lathe chuck and the pin presented to them while running, or the operation may be reversed, the pin being rotated and the cutter held stationary. If to be used by hand, hold them in a vise or clamp, or make a fixture to hold the pin, using a bit-stock for turning them for cutting.