ARTILLERY 793 vent is in the breech piece, which can be easily renewed when the former becomes enlarged. In the large muzzle-loading Armstrong guns the barrel or part surrounding the bore is made FIG. 9. Armstrong Gun. of solid steel tempered in oil, which diminishes brittleness and adds to the tenacity ; the barrel in rear of the trunnions is enveloped by three layers of wrought-iron tubes, not welded to- gether at the ends, but hooked to each other by a system of shoulders and recesses ; the tube around the barrel opposite the seat of the charge is called the breech piece, and is not made of spiral bars like the others, but has its fibres and welds longitudinal so as to resist the recoil of the barrel against the head of the breech plug screwed into the breech piece. The number of grooves in the breech-loaders is 34, and the twist one turn in 9 feet ; in the muzzle-loaders the grooves are from 3 to 10, and the twist from one turn in 30 to one turn in 38 calibres. The muzzle-loading Arm- strongs were formerly rifled upon the shunt system, in which the grooves are much wider than the buttons on the projectile, except near the bottom of the bore ; that part or side of the groove passed over by the projectile in passing down the bore is deep enough to ad- mit the buttons freely, while the other side is so shallow that the ends of the buttons are pressed against it as the projectile comes out, thereby forcing its centre or axis toward the axis of the bore. This system has altogether failed in calibres larger than the 9-inch, and was finally abandoned in 1870 even for small calibres. In 1865 the French soft-metal stud and bearing system of rifling was adopted for large muzzle-loading guns, under the name of the Woolwich system ; after seven years' trial it is not found to give general satisfaction, and will probably be changed. The Frazer gun is a modification of the Armstrong ; the number of coils being lessened, cheaper iron used for the outer coils, which are shrunk on with the trunnion piece, and the arrangement of shoul- ders and recesses, to prevent separation of the parts, being improved. Whitworth guns are made of a substance called "homogeneous iron," a species of low steel said to be made by melting short bars of Swedish iron and add- ing a small amount of carbonaceous matter. The smaller Whitworth guns are forged solid ; the larger built up with coils or hoops, which are forced on by hydraulic pressure, being made with a slight taper and the ends joined by screw threads. The hoops are first cast hollow and then hammered out over a steel mandrel, or rolled out in a machine like that used for forming wheel tire ; before receiving their final finish, they are subjected to an an- nealing process for three or four weeks, which, though making the metal very ductile, slightly impairs its tenacity; the breech pin is made with otfsets in such a way as to screw into the end of the barrel and the next two surrounding hoops, the breech in the larger guns being hooped with a harder and higher steel than that used for the barrel. The cross section of the bores of the Whitworth guns is a hexagon with rounded corners, and the twist is very rapid. The projectiles are very long, those intended for armor punching being made of hardened iron or steel with very thick flat heads to prevent glancing ; shells of this kind have no fuse, the bursting charge being ignited by the heat generated by the violent blow of the projectile on the plate ; the powder before being inserted is wrapped in one or more thick- nesses of flannel, thus interposing a slow con- ductor between it and the heated metal, and delaying the explosion until the shell has com- pleted its penetration. The principal Whit- FIG. 10. Whitworth Gun. worth guns are the 120, 70, and 12-pdrs. of 6*4, 5, and 2*75 inches diameter respectively, and firing 151, 81, and 12-lb. projectiles. The Blakely gun combines in its construction the principles of initial tension and varying elasticity, the object being to bring the strength of all the metal of the piece into simultaneous play to resist explosion. The inner tube or barrel is made of low steel, having considera- ble but not quite enough elasticity ; the next tube is made of high steel with less elasticity, and is shrunk on the barrel with just sufficient tension to compensate for the insufficient differ- ence of the elasticity between the two tubes ; the outer cast-iron jacket, to which the trunnions are attached, is the least elastic of all, and is put on with only the shrinkage obtained by warming it over a fire. The steel tubes are cast hollow and hammered over steel mandrels, under steam hammers ; by this process they are elongated about 130 per cent., and the tenacity of the
