Engineering Wonders of the World
Volume I

408 ENGINEERING WONDERS OF THE WORLD. “ built up ” of a series of hardened steel tubes placed one over the other while hot, and allowed to shrink by cool- Wir^=wound a pOS^ion of security. In the wire-wound method a tube,, the real “ barrel ” or “ bore ” of the finished gun, having a thickness varying from 1 to inches, is placed on a slowly turning lathe. Wire ribbon of a rectan- to that of spiral stairways. The grooves, by gripping the soft copper rings or “ driving bands ” affixed to the rear of the long shells, give to these last the twist that helps to maintain a rigid adherence to the direction imparted by the initial impulse. The muzzle of the gun is thickened somewhat to resist the final strain of release as the shell and its following propellant gases fly from the DIAGRAM TO SHOW THE PENETRATIVE POWERS OF GUNS OF VARIOUS CALIBRES. gular section is then wound carefully round it, coil by coil, until a sufficiency for the agreed pressure - strength has been reached. A retaining band is placed over the last coil to keep it in place, and the whole is covered with a steel jacket, which protects it and also gives longitudinal strength to the piece. The wire as it is wound on is sub- jected to a very high, tension. Upwards of 120 miles of such metal ribbon enters into the construction of a modern 12-inch gun. The inner tube or barrel is “ rifled ” along its entire length—that is, grooves are cut into its surface with a circular inclination similar are of larger The Breech- block. tube. Into the rear of the bore of the gun, the last few feet of which diameter for the better recep- tion of the cordite or powder, a “ breech-block ” or door is placed. A breech - block is of conical shape, and the threads or screws whereby it “ engages ” with the body of the gun itself, and so closes the firing chamber before the discharge, are so interrupted that the entire locking of the device is accom- plished by one-twelfth of a circle’s turn. The opening and shutting of this breech- block is effected by a wheel which, in one