Britain at Work
A Pictorial Description of Our National Industries

230 BRITAIN AT WORK. A WIRED GUN PLACED IN Photo i Gregory & Co., Strand, W.C. POSITION FOR RIFLING. occupies a week to a month, according to size, with the machine working continuously. The pitch of the rifling is progressive, and with a 43-ton gun the cutter will make one turn in every 30 feet. The cutter—which only cuts in coming out — goes up each groove from eight to twelve times, according to the hardness of the metal, and, as there are eighty grooves, in many instances it travels along the gun eight hundred times. The greatest conceivable care has to be exercised in the rifling of big guns, as the slightest departure from the true course may now destroy material and work worth together £10,000 or £12,000. The gun now remains to be “ chambered ” and fitted with the breech - screw. The chamber, which is enlarged by a subsequent boring after the bore is completed, is bottle- shaped ; it does not meet the bore abruptly, but the two diameters are joined by easy curves. The gunmaker seeks to avoid a long chamber, as it gives scope for wave action on the part of the powder-gas, with the result that excessive local pressures are created. The breech-piece of the big gun is connected with the breech-encl of the gun by a hinged platform. The breech - piece or breech-screw of the no-ton gun draws out from the gun on to a sliding tray. In all cases the breech-screw or breech-plug is fastened in the breech-end of the guns upon what is known as the interrupted screw system, that is, the breech- plug and the breech-end of the gun are cut into corre- sponding screw-grooves, only for these to be subsequently taken out to the extent of one-half in opposite quarter- sections, so that the breech- piece is easily pushed into the gun—the screw parts or the breech-piece passing into the indented sections of the breech-encl, and vice versa— and the screws drawn into each other by a lever. The interrupted screw is really an ingenious form of lock. The screw in our gun is 18 to 20 inches long. The fixing of the breech- piece demands great skill. The precision of the fit is a vital point. It is an absolute necessity to prevent the escape of the powder- gas from the powder-chamber through the breech-pieces. The escape of gas through the breech is prevented in this way: An annular canvas bag, filled with asbestos and suet, is placed between the front of the breech- screw and a strong steel bolt shaped like a mushroom and called from its shape “ the mushroom head.” When the gun is fired the pressure of the powder-gas forces the mushroom head back, compresses the canvas pad, and squeezing it outwards makes it bear closely against the interior of the gun, so that an escape of gas is impossible; when the projectile is clear of the gun, and the pressure is removed, the pad returns to its original condition by its own elasticity, and the breech-screw is easily withdrawn. The effectual closing of the breech so as to prevent the escape of gas has long been a problem whose difficulty is only surpassed by its importance, for it must be remembered that the powder-gas exerts the same enor- mous pressure upon the breech-piece as it does upon the projectile ; but that the Elswick Company have hit upon an efficient method is sufficiently proved by the fact that the British service guns are fitted on the same principle. The arrangements for firing the gun appear to be simple, but as a matter of fact