A curious and interesting part of the operation of manufacturing muskets is the straightening of the barrel. This straightening takes place continually in every stage of the work, from the time the barrel first emerges from the chaotic mass produced by heating the scalp, until it reaches the assembling-room, where the various parts of the musket are put together. As you enter the boring and turning rooms, you are struck with surprise at observing hundreds of workmen standing with musket-barrels in their hands, one end held up to their eyes, and the other pointing to some one of the innumerable windows of the apartment. Watching them a few moments, however, you will observe, that, after looking through the barrel for half a minute, and turning it around in their fingers, they lay it down upon a small anvil standing at their side, and strike upon it a gentle blow with a hammer, and then raise it again to the eye. This is the process of straightening.
In former times, a very slender line, a hair or some similar substance, was passed through the barrel. This line was then drawn tight, and the workman, looking through, turned the barrel round so as to bring the line into coincidence successively with every portion of the inner surface. If there existed any concavity in any part of this surface, the line would show it by the distance which would there appear between the line itself and its reflection in the metal. This method has not, however, been in use for over thirty years. It gave place to a system which, with slight modification, is still in practice. This method consisted in placing a small mirror upon the floor near the anvil of the straightener, which reflected a diagonal line drawn across a pane of glass in a window. The workman then placed the barrel of the musket upon a rest in such a position that the reflected line in the mirror could be again reflected, through the bore of the barrel, to his eye,—the inner surface of the barrel being in a brilliantly polished condition from the boring. When the barrel is placed at the proper angle, which practice enables the person performing this duty to accomplish at once, there are two parallel shadows thrown upon opposite sides of the inner surface, which by another deflection can be made to come to a point at the lower end. The appearance which these shadows assume determines the question whether the barrel is straight or not, and if not, where it requires straightening. Although this method is so easy and plain to the experienced workman, to the uninitiated it is perfectly incomprehensible, the bore of the barrel presenting to his eye only a succession of concentric rings, forming a spectacle of dazzling brilliancy, and leaving the reflected line in as profound a mystery after the observation as before.
At present, the mirror is discarded, and the workman holds the barrel up directly to the pane of glass, which is furnished with a transparent slate, having two parallel lines drawn across it. The only purpose subserved by the mirror was that of rendering the operation of holding the barrel less tiresome, it being easier to keep the end of the musket presented to the line pointing downwards than upwards. Formerly, this means of detecting the faults, or want of straightness in the barrel, was, like the working of the rolling-mill, the secret of one man, and he would impart it to no one for love or money. He was watched with the most intense interest, but no clue could be obtained to his secret. They gazed into the barrel for hours, but what he saw they could not see. Finally, some fortunate individual stumbled upon the wonderful secret,—discovered the marvellous lines,—and ever since it has been common property in the shop. Each workman is obliged to correct his own work, and afterwards it is passed into the hands of the inspector, who returns it to the workman, if faulty, or stamps his approval, if correct. The next process is that of grinding, for the purpose of removing the marks left upon the surface by the tool in turning, and of still further perfecting its form. For this operation immense grindstones, carried by machinery, are used, which rotate with great rapidity,—usually, about four hundred times in a minute. These stones are covered with large, movable wooden cases, to keep the water from flying about the room, or over the workmen.
An iron rod is inserted into the bore of the barrel, and is fitted very closely. The rod is furnished with a handle, which is used by the workman for holding the barrel against the stone, and for turning it continually while he is grinding it, and thus bringing the action of the stone upon every part, and so finishing the work in a true cylindrical form. In the act of grinding, the workman inserts the barrel into a small hole in the case in front of the stone, and then presses it hard against the surface of the stone by means of an iron lever which is behind him, and which he moves by the pressure of his back. The work is very rapidly and smoothly done.
There are twelve sets of stones in the grinding-room in constant operation day and night. These stones, when set up, are about eight feet in diameter, and are used to within twelve inches of the centre. They last about ten days.
The operation of grinding was formerly regarded as a very dangerous one, from the liability of the stones to burst in consequence of their enormous weight and the velocity with which they revolve; but, about twenty years since, a new method of clamping the stone was adopted, by means of which the danger of bursting is much diminished. The last explosion which took place in this department occurred about nine years ago. The operation of grinding, however, is objectionable also from the very unhealthy nature of the work. Immense quantities of fine dust fill the air, and the premises are always drenched with water, making the atmosphere damp and unwholesome.
In former times, it was customary to grind bayonets as well as barrels; but the former are now milled instead, thus making an important saving in expense, as well as gain in the health of the establishment. No mode, however, has yet been devised for dispensing with the operation of grinding the barrel; but the injury to the health, in this case, is much less than in the other.
When the barrels are nearly finished, they are proved by an actual test with powder and ball. To this purpose a building at the water-shops, called the proving-house, is specially devoted. It is very strongly built, being wholly constructed of timber, in order to enable it to resist the force of the explosion within, and contains openings in the roof and at the eaves for the escape of the smoke, a very large number of barrels being proved at once.
The barrels are subjected to two provings. In the first, they are loaded with a double charge of powder and two balls, thus subjecting them to a far greater strain than they can ever be exposed to in actual service. In the second proving, only the ordinary charge is used.