~THINGS TO KNOW ABOUT A BIG GUN~ Before going into a description of the manufacture of a big gun it would be well to understand the following definitions: The “breech” of a gun is its rear-end, or that end into which the projectile and powder charge are loaded. The “muzzle” of a gun is its forward end. By “calibre” is meant the inside diameter of the gun in inches. A 5-inch gun is one of “minor calibre,” and one of 14-inches a gun of “major calibre.” The length of a gun is never expressed in inches or feet, but in the _number of times_ that its calibre is divisible into its length; thus, when we say a 12-inch 50-calibre gun, we mean a gun of 12 inches in diameter, and 12 times 50, or 600 inches long. The “bore” is the hole extending through the center of the gun, from the rear face of the liner to its forward end. The “powder chamber” is the rear part of the bore, and extends from the face of the breech plug when closed to the point where the “rifling” begins. The powder chamber is slightly larger in diameter than the rest of the bore. The “rifling” is the name given to the spiral grooves which are cut into the surface of the bore of the gun, and give to the projectile its rotary motion when the gun is fired. With the advent of “iron-clads” and heavily armored fortresses, it became necessary to increase the power of the guns in use, until to-day a 14-inch gun of 45 calibres fires a projectile weighing 1400 pounds, with an initial velocity of 2600 feet per second. An idea of this initial velocity may be better obtained by comparison when you realize that a train going sixty miles an hour is only traveling at the rate of 88 feet per second. Now, in order to produce such wonderful power in a gun, great pressure must be generated in the bore, and it was soon found that a one-piece gun, whether cast or forged, could not withstand such pressures.