MARTINI-HENRY RIFLE.
This rifle combines the Peabody-Martini action and Henry rifling. This excel lent rifling, gives ta bearing faces for the bullet. The g,rooves are 7 in number and are .007 inch in depth. The fabrication of this rifle involves many departures from the usual processes and operations. The barrel is made of soft or mild steel prepared by the "Siemens-Martin- process, this metal having been found to be of a very uniform nature. The barrel bars or molds are obtained by contract in leng,ths of r5 inches, the diameter for rifle bars being 1-2 11161. Tile barrel bar is heated to a white heat and passed throug,h the barrel rolling,-mill, which consists of ten pairs of rolls arranged alternately horizontally and vertically, when it is drawn out in one heat to the full length required (about 36 inches), taper in form and solid. The barrels while being drilled are placed vertically in a machine, where they revolve with a speed of 300 revolutions per minute, the holes already made at each end acting as guides for the set of three drills used in this operation. The method of using these drills insures a long hole of small diameter being drilled perfectly true, and until this method \vas tried and adopted this was found to be a most difficult task. The drills consist of, first, "the core-drill,- for roughly cutting away the metal. This is run in half an inch, when the bariel is taken out and emptied of scarf or cuttings by placing, it over a jet-pipe, when a strong stream of washing liquor thoroughly clears out the bore. Another half inch is drilled in the same manner, and the bore again washed out. The second drill or half-round bit is 110W 11SC(i, ThiS drill is 0.430 inch in diameter, and having only a cut of 0.05 inch to make in clearing the hole, is run down thc one inch the core-drill has cleared without any risk of deviating, from the truth. The barrel is then again washed out and No. 3 drill made use of. This has a stock fitting, the hole already bored, and ending in a small 3-16 inch drill, which, being supported by the stock, drills away the center perfectly true with the axis of rotation, ready for the "core or "roug,ning drill- to start again. f this system is rigidly 'carried out inch by inch it is possible to drill a hole three or four feet deep with an error of less than 0.005 inch.
The next operation is to support and hold the bore true while the outside is turned perfectly concentric with it. .\ fter a number of experiments to rind out a means of fixing a !nu- Ilinicd bush or collar on a rough exterior. the method of
running sulphur in a liquid state between the barrel and bush was adopted. Ily this means the exterior of a barrel caii he turned perfectl true with the bore without injury to the inside. The barrel is placed vertically, when two plugs, who,se mitres coincide v, ith the axis of the barrel are placed in the breech and muzzle; the bush is then held over it and melted sulphur is poured in between barrel and bush. This gives a bearing for the outside perfectly true with the bore.
The rifling is done with a cutter having a head of suitable form for the rifling required. This is fitted into a groove cut in a box about eight inches in length and fitting the bore. Tt is drawn through the barrel by a rod fastened to one end of the cutter box, the other end of the rod being coupled into the spindle of the head stock or traversing saddle. On the spindle is a pinion geared into a sliding rock carried by the same saddle. The end of the rack is fitted to slide backwai (I and forward along, a fixed bar, which can be set at any angle necessary to rotate the spindle and cutter box to the amount of spiral required. From four to five cuts are needed for each groove, and the cutter is fed up by a screw tapped into the end of the cutter box. to which a rod is attached, which works through the center boss of a hand wheel. A spiral groove is cut along, this rod, in which a feather fixed in the boss of the hand wheel slides, enabling the feed-screw to be screwed in or out by the hand wheel as required. An index is connected with the hand wheel, enabling the operator to read off the depth of cut. The barrel is fixed in a rotating chuck, which is divided so that any number of grooves required can be cut inside the bore. The rifling is of uniform twist of in 22 inches, or one and a half turns in the length of bore (33 inches).
A particular form of emery wheel, called a "rim wheel,- is employed for finish ing up some of the components. Its use has enabled unskilled labor to take the place of a high class-of skilled 1.vorkmen, and the work is better finished. For instance, the slot of the back-sight leaf is first drifted to its true size. By this it is held in a fixing_, attached to a vertical axis ,and both edges with cap attached can be passed across the face of the rim wheel, maintaining it perfectly true, and grinding the edges of the leaf and cap parallel to each other. The sides are done in the same manner. See Peabodv Rific and Peabody-ilartini Ritic.