A fire-arm or weapon chiefly composed of a barrel or long tube, from which shot and other missiles are discharged by means of inflamed gunpowder; ignition being effected by the percussion of flint and steel, or that of detonating powder, through the instrumentality of a piece of mechanism called the lock, which is fixed to the handle or stock, and in connexion with the lower extremity of the barrel, where the charge is deposited. The word gun, however, is indiscriminately applied to almost every species of fire-arm, and is usually divided into two classes, namely, great guns, and small arms. The former include cannon, artillery, and various species of ordnance, that are moved on wheels, pivots, trucks, and slides, which are described under their separate heads; the latter class, which embraces muskets, blunderbusses, carbines, fowling-pieces, and pistols, being such as are manufactured by gun-smiths, we propose to describe in this place.

The principal parts of a gun are the barrel, the lock, and the stock. The following are the requisite properties of the barrel: - first, lightness, that it may incommode the person who carries it as little as possible; secondly, sufficient strength, and other properties requisite to prevent its bursting by a discharge; thirdly, it should be constructed in such a manner as not to recoil with violence; and fourthly, it should be of sufficient length to carry the shot to as great a distance as the force of the powder employed is capable of doing. The best barrels in this country are formed of stubs, as they are called, or old pieces of horse-shoe nails. About twenty-eight pounds of these are requisite to form a single musket barrel. The method of manufacturing them from this material is as follows: - a hoop of about an inch broad, and six or seven inches diameter, is placed in a perpendicular position, and the stubs, previously well cleaned, piled up in it with their heads outermost on each side, till the hoop is quite filled and wedged tight with them.

The whole then resembles a rough circular cake of iron, which being heated to a white heat, and then strongly hammered, unite into one solid lump.

The hoop is now removed, and the heatings and hammerings repeated till the iron is rendered very tough and close in the grain, when it is drawn out into pieces of about twenty-four inches in length, half an inch or more in breadth, and half an inch in thickness. Four of the pieces, prepared as has been described, are required for one barrel; but in the ordinary way, a single bar of the best soft iron is employed. The workmen begin with hammering out this into the form of aflat ruler, having its length and breadth proportioned to the dimensions of the intended barrel. By repeated heating and hammering, this plate is turned round a tempered iron rod called a mandril, the diameter of which is considerably smaller than the intended bore of the barrel. One of the edges of the plate being laid over the other about half an inch, the whole is heated and welded by two or three inches at a time, hammering it briskly, but with moderate strokes, upon an anvil, which has a number of semicircular furrows in it, adapted to the barrels of different sizes. Every time the barrel is withdrawn from the fire the workman strikes it gently against the anvil once or twice in a horizontal direction.

By this operation the particles of the metal are more perfectly consolidated, and every appearance of a seam in the barrel is obliterated. The mandril being then again introduced into the cavity of the barrel, the latter is very strongly hammered upon it m one of the semicircular hollows of the anvil by small portions at a time, the heatings and hammerings being repeated until the whole barrel has undergone the operation, and its parts rendered as perfectly continuous as if they had been formed out of a solid piece. To effect this completely three welding heats are necessary when the very best iron is made use of, and a greater number for the coarser kinds.

The next operation in forming the barrels is the boring of them, which is usually done in the following manner: - Two beams of oak, each about six inches in diameter, and six or seven feet long, are placed horizontally, and parallel to one another, having each of their extremities mortised upon a strong upright piece about three feet high, and firmly fixed; a space of three or four inches is left between the horizontal pieces, in which a piece of wood is made to slide by having at either end a tenon let into a groove, which runs on the inside of each beam throughout its whole length. Through this sliding piece a strong pin or bolt of iron is driven or screwed in a perpendicular direction, having at its upper end a round hole large enough to admit the breech of the bane], which is secured in it by means of a piece of iron that serves as a wedge, and a vertical screw passing through the upper part of the hole. A chain is fastened to a staple on one side of the sliding piece, which runs between the two horizontal beams, and passing over a pulley at one end of the machine, has a weight hooked on to it; an upright piece of timber is fixed above this pulley and between the ends of the beams, having its upper end perforated by the axis of an iron crank furnished with a square socket, the other axis being supported by the wall, or by a strong post, and loaded with a heavy wheel of cast-iron to give it force.

The axes of this crank are in a line with the hole in the bolt already mentioned. The borer being then fixed into the socket of the crank, has its other end, previously well oiled, introduced into the barrel, whose breech part is made fast in the hole of the bolt; the chain is then carried over the pulley, and the weight hooked on; the crank being then turned with the hand, the barrel advances as the borer cuts its way till it has passed through the whole length. The boring bit consists of an iron rod somewhat longer than the barrel, one end of which fits the socket of the crank; the other is adapted to a cylindrical piece of tempered steel, about an inch and a half in length, having its surface cut after the manner of a perpetual screw, with five or six threads, the obliquity of which is very small; the breadth of the furrows is the same with that of the threads, and their depth sufficient to let the metal cut by the threads pass through them easily; thus the bit gets a strong hold of the metal, and the threads being sharp at the edges, scoop out and remove all the inequalities and roughness from the inside of the barrel, and render the cavity smooth and equal throughout.