All these weapons were rifled, so that there was of necessity a corresponding difference in the projectile employed. Conical shells being used, studs were now placed on the body of the shell to fit into the rifling grooves, which were made few in number and deeply cut. This was apt to weaken the bore of the gun; but on the other hand many studs to fit into several shallow grooves weakened the cover of the shells.
Various modifications were tried, and finally a gas-check which expands into the grooves was placed at the base of the shell.
The muzzle-loader having thus been turned into a very efficient modern weapon the next problem to be solved was how to throw a projectile with sufficient force to penetrate the iron and steel armour-plates then being generally applied to war-ships. “Build larger guns” was the conclusion arrived at, and presently the arsenals of the Powers were turning out mammoth weapons up to 100 tons, and even 110 tons in weight with a calibre of 16 inches and more for their huge shells. Then was the mighty 35-ton “Woolwich Infant” born (1872), and its younger but still bigger brothers, 81 tons, 16-inch bore, followed by the Elswick 100-ton giants, some of which were mounted on our defences in the Mediterranean. But the fearful concussion of such enormous guns when fixed in action on board ship injured the superstruction, and even destroyed the boats, and the great improvements made in steel both for guns and armour soon led to a fresh revolution. Henceforward instead of mounting a few very heavy guns we have preferred to trust to the weight of metal projected by an increased number of smaller size, but much higher velocity. And these guns are the quick-firing breech-loaders.
The heaviest of our up-to-date ordnance is of moderate calibre, the largest breech-loaders being 12-inch, 10-inch, and 9.2-inch guns. But the elaborateness of its manufacture is such that one big gun takes nearly as long to “build up” as the ship for which it is destined. Each weapon has to pass through about sixteen different processes:—
(1) The solid (or hollow) ingot is forged.
(2) Annealed, to get rid of strains.
(3) It is placed horizontally on a lathe and rough-turned.
(4) Rough-bored in a lathe.
(5) Hardened. Heated to a high temperature and plunged, while hot, into a bath of rape oil kept cold by a water-bath. It cools slowly for seven to eight hours, being moved about at intervals by a crane. This makes the steel more elastic and tenacious.
(6) Annealed, i.e. reheated to 900° Fahr. and slowly cooled. Siemens’ pyrometer is used in these operations.
(7) Tested by pieces cut off.
(8) Turned and bored for the second time.
(9) Carefully turned again for shrinkage. Outer coil expanded till large enough to fit easily over inner. Inside, set up vertically in a pit, has outside lowered on to it, water and gas being applied to make all shrink evenly. Other projections, hoops, rings, &c., also shrunk on.
(10) Finish—bored and chambered.
(11) Broached, or very fine bored, perhaps lapped with lead and emery.
(12) Rifled horizontally in a machine.
(13) Prepared for breech fittings.
(14) Taken to the Proof Butts for trial.
(15) Drilled for sockets, sights, &c. Lined and engraved. Breech fittings, locks, electric firing gear, &c., added. Small adjustments made by filing.
(16) Browned or painted.
When worn the bore can be lined with a new steel tube.
These lengthy operations completed, our gun has still to be mounted upon its field-carriage, naval cone, or disappearing mounting, any of which are complicated and delicately-adjusted pieces of mechanism, the product of much time and labour, which we have no space here to describe.
Some account of the principal parts of these guns has already been given, but the method by which the breech is closed remains to be dealt with.
It will be noticed that though guns now barely reach half the weight of the monster muzzle-loaders, they are even more effective. Thus the 46-ton (12-inch) gun hurls an 850-lb. projectile with a velocity of 2750 foot-seconds, and uses a comparatively small charge. The famous “81-ton” needed a very big charge for its 1700-lb. shell, and had little more than half the velocity and no such power of penetration. This change has been brought about by using a slower-burning explosive very powerful in its effects; enlarging the chamber to give it sufficient air space, and lengthening the chase of the gun so that every particle of the powder-gas may be brought into action before the shot leaves the muzzle. This system and the substitution of steel for the many layers of welded iron, makes our modern guns long and slim in comparison with the older ones.