In order to secure regular and uninterrupted movement of the projectile through the bore it is necessary that the projectile and bore have the same geometric axis. Also the projectile must be seated exactly and uniformly for succeeding rounds in its seating in the bore. This latter is necessary in order that the powder chamber may not vary as this would give irregular pressures. The liability of _strapping the rotating bands_ or setting off the fuze in certain kinds of fuzes are also explained by inertia. It might even cause sufficient shock to detonate the charge in the shell. The remedy is accurate seating of each projectile by reason of trained gun crews using the same amount of force at each ramming. The first condition, coincidence of axes, is obtained by means of the ogival head which has a diameter some tenths of a millimeter smaller than the diameter of the bore, and serves as a front support for the projectile while the rotating bands center it in rear. Were it not for the bell the projectile, held only by the soft material of the rotating band, would wabble in its travel through the bore and tumble soon after leaving it. It is also necessary that the center of gravity of the projectile be on its geometric axis. Otherwise it will travel on a spiral of the same pitch as the grooves and knock the tube walls as it travels through the bore and without the support of the bell might cause a premature explosion by actuating the fuze. [Illustration: _155M/M SHRAPNEL—95 LBS.—MARK-I._] [Illustration: COMMON STEEL SHELL MARK I. COMMON STEEL SHELL MODEL OF 1905. SHRAPNEL. CARTRIDGE CASE. 4.7” Gun Ammunition.] Three-inch Ammunition. =Fixed ammunition= is used in the 3” field guns, and is made up with either common shrapnel, high explosive shrapnel, or common steel shell. The rounds as made up vary in length with the type of projectile used. The ammunition chests of the battery are of sufficient size to take any one of the rounds furnished, so that the number of each kind to be carried is a matter for regulation by proper authority. Each round is issued with projectile filled and fused. The weight of the projectile is 15 pounds, and the total weight of one round is 18.75 pounds. The components of one round are _the cartridge case with primer, the powder charge, igniter, projectile and fuze_. =The cartridge case.=—The cartridge case is a solid drawn-brass case 10.8 inches long; it has a capacity of 66.5 cubic inches, and weighs, with primer, 2.25 pounds. A circular groove is cut in the base of the cartridge case and _the groove is painted red for high explosive shrapnel, yellow for common shrapnel, and black for high explosive shell_. =The primer.=—The percussion primer, known as the “110-grain percussion primer,” contains an igniting charge of 110 grains of black powder in addition to the essential elements of a percussion primer. The purpose of the black powder is to insure the ignition of the smokeless powder charge in cartridge case.