Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/304

Rh GUNMAKING rupps mstruc- much. The interior of the recent German gun is a steel tyke ag m ^ Q Armstrong construction, but it is very much thicker and forms the body of the piece, instead of being chiefly used to provide a sound surface for the bore. It is thickest over the powder and shot chambers, tapering towards the muzzle (fig. 40). Over the thickest part, and in some guns over a considerable portion of the chase, hoops of cast steel are shrunk on, the shrinkage being adjusted FIG. 40. Section of Krupp Gun. to bring the strength of the outer hoops into play to sup port the body of the gun on discharge. The number of hoops depends on the size of the gun and the severity of the strain it has to withstand ; they are usually much more numerous than the English coils, and the section of a heavy Krupp gun presents somewhat the appearance of a stone wall It is believed that the steel is not toughened in oil, but the details of manufacture have not as yet been made public. Steel of the excellent quality employed by Krupp is un doubtedly a stronger material than wrought iron ; its present trustworthinesss is, however, of late date, and it has hardly gained the general confidence accorded to wrought iron. Possibly the method of construction adopted by Krupp, containing as it does a number of unwelded joints, scarcely permits the several parts of the guns to support each other as efficiently as is the case with the magnificent forgings of the coil system ; be this as it may, the German pieces, though made of stronger and more ex pensive material than the English ones, are just as heavy for any given power, proportions and ammunition being similar. In France and Italy a combination of cast iron and steel has been introduced with a view to economy. The interior of the gun is a moderately thick steel tube as in the coil guns ; over this is a thick cast-iron body, corresponding to the steel body of the Krupp guns. On the exterior are shrunk steel hoops. Sir J. Whitworth uses his fluid-compressed steel for the manufacture of ordnance. He forces massive hoops over a central tube, and over one another by hydraulic pressure or by shrinkage. Mr Vavasseur employs Firth s crucible steel for his guns, which are built up somewhat in the same way as Krupp s. He also uses exterior coils of wrought iron in some patterns. /Systems of Loading. The comparative advantages of breech-loading and muzzle-loading for ordnance on service are fully discussed in the article GUNNERY. We have now to mention the principal modes of closing the breech, either permanently as in muzzle-loaders, or temporarily as in breech-loaders. The former is comparatively a simple matter. When the whole gun, or the interior of it, is formed of cast metal, iron, bronze, or steel, the block is merely bored to the required depth, and the end left un- bored to form the breech. Should the inner part of the gun be formed of wrought material, such as coils, it becomes necessary to close the end with some device which shall render it gas-tight and strong. Several kinds of cups and plugs have been tried for this purpose, the most successful of which is the cup already mentioned in the description of the converted guns. When we come to the temporary closing of the end of the bore demanded by breech-loading, a far more difficult problem presents itself. This problem has been more or less satisfactorily solved in a great variety of ways, but it will be sufficient to examine the three principal types or systems of breech-loading employed in modern artillery. They are popularly known as the Armstrong, the Krupp, and the French systems. The Armstrong system is the earliest of these in point of Arm- date. In it a slot is cut through the top of the breech of stron i the gun into the tube at A (fig. 41) ; a breech block (fig. Jj&quot; 43), through which the vent is driven, is dropped into this ^^ I itu i ] - T 1 P ft 1 &amp;gt;5. i /~^ 1 ~ l 7 * s V17 - 7 T| i j 1 i J c ! II S---15V75 3 t u:-..-. . _. T*-* ~- B* (a v &amp;lt; S2: a FIG. 41. 7-inch Armstrong Breech-loader. slot, and is pressed firmly against the bore from behind by the breech screw (fig. 42), which is provided with two powerful lever handles for the purpose. Where the breech block, or vent piece, as it is usually called, presses against the lip of the bore, both surfaces are of copper, and are re newed from time to time as channels are worn through between them by the rush of the escaping powder gas. There are many guns, from 6-pounders to 7-inch, made on FIG. 42. Breech Screw. FIG. 43. Vent Piece. this plan in the British service, and at the time of their intro duction they constituted a great advance in gun construc tion. Experience in the field and at practice has, however, revealed many grave faults in them. No joint consisting simply of two abutting surfaces can be made so tight as to prevent the gas from escaping on the discharge of the piece ; the pressure in the powder chamber is so great that a con siderable expansion takes place for the moment, and per mits a fan of flame to flash out. The eroding effects of gas in motion at high pressure are extraordinarily destructive, and constant necessity for repair arises from this cause. It has also been found that in rapid firing the breech screw may be too quickly forced home, nipping the vent piece before it has fallen into its proper position ; the end of the bore is then not sealed, and important and perhaps danger ous accidents occur. Moreover, even with moderate-sized ordnance, the vent piece becomes too heavy for convenient lifting. In the Krupp system (fig. 44), a slot is cut through both sides of the breech of the gun ; in this slot, in the latest patterns, runs a cylindro-prismatic wedge, or, in other words, a wedge of D section, the round side to the rear. The flat side forms the bottom of the bore. For loading, the wedge is pulled out to the left side of the piece as far as the stop will allow it to go, the shell and cartridge are thrust up the gun from behind, the wedge is pushed in, and is pressed hard home and secured by an ingeniously- contrived screw with powerful handles. As was mentioned with regard to the Armstrong system, no amount of pressing home and securing would by itself be of any avail in pre-