On this system (fig. 11) wrought iron coils had been shrunk over one another in order that the internal tube, or barrel, was positioned in a state of compression and the outer parts in a state of tension-the parts so proportioned that each performs its maximum duty in resisting the stress from inside. These outer coils were shrunk over a hollow breech-piece of solid iron, having the fibre running lengthwise to resist the longitudinal stress. It is simple to show that any so-known as homogeneous gun, i.e. a gun product of solid materials and never built up, quickly reaches a restrict of thickness past which extra thickness is virtually ineffective in giving energy to resist circumferential stress. This is due to the fact that the stress on the metal close to the bore is way increased than that' on the outer portion and shortly reaches its maximum resistance which further thickness of steel does not materially increase.

The interior layers of the metal are thereby compressed so that the fuel pressure has first to reverse this compression after which to extend the metal. The gun barrel supported by the contraction of the outer hoops will then be able to endure a gas pressure which will be expressed as being proportional to the initial compression plus the extension, whereas in the old kind solid gun it was proportional to the extension solely. One of the earliest was the Hotchkiss (1865) shell (fig. 27), in which a separate base end B was pushed forward by the gas strain and squeezed out the lead ring L into the rifling. After loading, the block was dropped into its place and the breech screw turned quickly in order that it'd jam the block against its seating, and so stop the escape of powder fuel when the gun was fired. Even with feeble gunpowder this means of securing the chamber doesn't commend itself, however as powder improved there was a greater chance of the breech end of the gun giving means; besides which the escape of the powder gas from the imperfect joint between the chamber and gun will need to have caused great inconvenience.

Accidents will need to have been frequent, and improvements have been made by dropping the breech or chamber of the weapon into a receptacle, solidly forged on or fastened by lugs to the rear end of the gun (fig. 7). This system was used for small guns solely, resembling wall items, &c., which couldn't be simply loaded on the muzzle owing to the place by which they had been placed, and in order to obtain rapidity each gun was furnished with a number of chambers. The coned breech screw is formed with the entrance part conical and the rear cylindrical, to facilitate its entrance into the gun, and also its exit; this form, furthermore, is taken advantage of by reducing the interruptions in the screwed surface alternately on the coned half and on the cylindrical half, so that there's a screwed floor all round the circumference of the breech screw. The gun (fig. 10) had a removable breech block having on its entrance face a coned copper ring which fitted right into a coned seating at the breech finish of the powder chamber. Fig. 11.-Armstrong B.L. Construction. B.L. guns. In Q.F.

Fig. 10.-Armstrong B.L. Arrangement. The strategy of boring is illustrated in fig. 17. The barrel or hoop A, to be bored, is handed by way of the revolving headstock B and firmly held by jaws C, the other end being supported on rollers D. A head E, mounted on the tip of a boring bar F, is drawn regularly through the barrel, as it revolves, by the leading screw K actuated by the gear G. The boring head is supplied with two or extra cutting tools, and in addition with a variety of brass pins or pieces of arduous wooden to act as guides, so as to keep the boring head central after it has entered the barrel. On the set off being pulled by a lanyard the striker is released and fires the tube. The a number of cylinders were shrunk over the steel inner tube or barrel. It is then wound on a drum, prepared for the next process, which consists in drawing it by graduated holes made in a hardened steel draw-plate, the wire being usually annealed and pickled during this course of. The first to employ efficiently this vital principle for all parts of a gun was Lord Armstrong (q.v.), who in 1855-1856 produced a breech-loading subject gun with a steel barrel strengthened by wrought iron hoops.

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