in the process of manufacture must be semi-automatic at least and, consequently, the organization of the shop and the machines having been adjusted with that object, the labour employed must be arranged for purely repetition work, for which it can be trained easily and quickly.
Having regard to this, and to the capacity of an ordinary engi- neering shop, it is essential to allocate only a certain number of stages in any one process to any one workshop, suitably arranging the stages to the power of that shop.
The machines mostly to be found in an engineering shop can gen- erally be adapted for any of the operations required in the machin- ing of shell. The ordinary engine lathe can be easily converted for the boring and machining of larger shell, and drilling machines and turret lathes for the same operations with smaller shell. The main point to be considered is the provision of suitable jigs and gauges to enable every operation to be performed by semi-skilled labour in rapid repetition. For hydraulic-press forging of bodies of shell and for the pressing on of driving bands, however, the machines neces- sary are not usually to be found in the ordinary engineering shop; and as it is not easy to find substitutes on account of the high pres- sure requisite in working, and the manner in which it is necessary to apply that pressure, arrangements for these operations have to be made specially. But with a certain few specially arranged shops of such nature, a supply of part-wrought material could be easily put out sufficient to keep fully employed a relatively large number of ordinary engineering shops adapted for the machining operations.
(F. M. R.)
CARTRIDGES AND PRIMERS FOR ORDNANCE
Cartridges for ordnance may be divided into two main classes technically called " breech-loading " and " quick-firing " and each class subdivided into gun and howitzer cartridges. All guns are nowadays breech-loaders, and the main classes men- tioned above are termed B.L. or Q.F. in reference to the system of " obturation " (breech-sealing) employed with the gun. With the B.L. obturation is effected by the breech mechanism, while with the Q.F. it is effected by the cartridge case.
The envelope of cartridges for B.L. guns must be of a material which will stand wear and tear when filled, not deteriorate from chemical action of the explosive while in store, not have injurious effects on the explosive, and be entirely consumed in the gun when the charge is fired, leaving no debris smouldering in the gun after the charge has been fired. Silk cloth made from the refuse silk from the outside of cocoons has been found to be the best material for the purpose.
The propellant explosive, according to the nature of the gun, is either cordite, N.C.T. (nitrocellulose tubular), or ballistite.
AU smokeless powders are somewhat difficult to ignite in a gun. Therefore, to make ignition certain and to prevent hang fires an igniter of fine grain gunpowder is used with every cartridge. This powder is enclosed in a bag of shalloon, which is attached to the cartridge in such a position as to intercept the flash from the tube.
Prior to the use of any batch of propellant for cartridges, it is necessary to prove the propellant, as received from manufacture, in order to ascertain whether it conforms to specification require- ments. In a chemical test a small amount is subjected to certain analytical tests. In a ballistic test a certain number of charges, made up according to the intended design of cartridge, is fired in a comparative trial against a like number of similar charges ol a batch of propellant known as a " current standard." Current stand- ards are compared in a similar manner with a " master standard," the ballistics of which have been ascertained under certain specific conditions. By this comparison, both in the velocities given to the projectile and in the pressures given in the gun, the variation from the standard is found for the batch, and any adjustment in the weight of the charge necessary for the intended cartridge can be determined.
B.L. cordite cartridges are built up of bundles of cordite in the form of sticks cut to the required lengths, and the bundles are tightly tied with silk and inserted into silk cloth bags, of which the ends are closed by discs of similar cloth. An igniter is stitched on to one or both ends of the cartridge. The exterior is laced with silk cloth tape so as to form a stiff cartridge. The charges for heavy guns are made up in separate portions containing half and quarter charges for convenience of handling and to allow of a reduced charge being used. For some of the longer guns the exterior of the cartridge is made cone-shaped, the coned form being produced by building up layers round a cylindrical core. In large cartridges a silk cloth becket runs up the centre and has a loop at the top for handling.
N.C.T. and ballistite have been used only for cartridges for smaller natures of guns. The method of making-up need not be described here; but it may be pointed out that, not being like cord-
ite, in the form of sticks, they do not make up into such compact cartridges, and that ballistite does not need an igniter.
For howitzers, variable charges are required, and cartridges must be built so that charges can be readily altered. Moreover, since a howitzer is shorter than a gun of the same calibre a lighter charge of cordite of smaller size is required, to ensure the charge being usefully consumed before the projectile leaves the barrel. The car- tridge is formed of a mushroom-shaped core made up in a bag to which the igniter is attached. On the stalk, so as to be easily remov- able, are placed the remaining portions of the cartridge made up in the form of rings, attached to the stalk by silk braids or light sew- ing. The weight of cordite in the rings is so graduated that by de- taching one or more, the varying charges required can be obtained.
With Q.F. cartridges the charges are contained in brass cases. This class of ammunition is of two types: (i.) " fixed ammunition" in which the projectile is fitted into the mouth of the brass case, thus closing it; (ii.) "separate ammunition" in which the projectile is separate from the cartridge. The brass case itself effects obtura- tion in the gun, for, when the cartridge is fired, the case expands slightly and tightly fits the chamber of the gun, thus preventing any escape of gas through the breech.
The use of the brass case influences rapidity of fire in that it obvi- ates the necessity for sponging out the gun after each round to remove smouldering debris; it allows of the cartridge carrying its own means of ignition, so avoiding the separate operation required with B.L. cartridges. The brass case also offers the advantage of greater safety against the risks of catching fire, and double loading of a gun is an impossibility.
This class of cartridge is especially useful for smaller natures of guns; but with larger natures of guns the rate of fire is nowadays not appreciably affected.
On the other hand the expense of the brass case is a serious con- sideration; and should a case, by reason of a flaw or split, fail to effect obturation, serious damage may be .caused to the gun. Fur- ther, in emergencies, failure in the supply of brass might seriously hamper output. 1 The brass case causes a large increase in weight to the cartridge, and so entails increase in means of transport. And as, to save material and expense, fired cases are collected, repaired and used several times over, considerable labour is involved in the salvage and transport.
The use of Q.F. ammunition has been restricted in the British service principally to smaller natures of guns; but the Germans have employed metallic cartridge cases for the largest natures of guns, probably on account of the difficulty in ensuring trustworthy obturation by any other means practicable with sliding-wed^e breech mechanisms, and also in the naval service owing to their giving greater safety from premature ignition.
The manufacture of the brass case is a lengthy process and requires care to ensure satisfactory results. The case is made from a disc of suitable thickness, which, being pressed through dies by hydraulic power, is shaped first into a cup and then gradually into a solid-ended cylinder. In order to relieve the stresses set, up the case is annealed between each draw. The head of the case is machined round the solid end to form a rim, by means of which extraction by the breech mechanism of the gun is effected. And, after having been passed through a die to give the taper required to allow of easy loading, the case is subjected to the final operation of machining to specified dimensions and to prepare the central hole in the head for reception of the means of ignition.
Charges for Q.F. cartridges are made up similarly to those for B.L. cartridges. Where necessary distance pieces of papier mache tube and felt wads are used to fill up the space in the case, and so prevent any movement of the charge. The lower end of the charge is splayed out to fit round the hole for the means of- ignition, and in cases where this is a cap a small igniter of powder enclosed in a shalloon bag is placed next the flash hole of the cap in order to increase its effect.
With fixed ammunition the mouth of the brass case is closed by the projectile, which is covered on the outside, below the driving band, with a cement to give a water-tight joint, and retained in position either by the lip of the case being pressed over a slightly coned portion prepared on the projectile, or by indentations in the lip of the case being pressed into a groove on the periphery of the projectile. With separate ammunition a cardboard disc and felt pad are inserted above the charge, and then a lid of white metal retained in position by small tongues turned down from the lip of the case.
For cartridges for Q.F. howitzers the charge is made up simi- larly, but as the charges must be easily adjustable separate ammuni- tion must always be used, and the cartridge arranged so that the lid of the case may be easily removable. The mouth of the case is closed by a removable cup-shaped cardboard disc, and sometimes, as a greater protection against moisture, by an india-rubber cap which fits tightly round the mouth of the case (see fig. l).
In order to reduce the flash on discharge of a gun anti-flash charges have been under experiment. A small charge of ammonium
1 Towards the end of the World War steel cartridge cases were employed by the Germans as a substitute for brass, but only for rifles and to some extent for light machine-guns. (C. F. A.)
