395. It is very important that dirt, sand, or other foreign substances should not be carried into the gun on the sponge or the projectile, or by the wind in batteries on shore.
In using guns on shore, a canvas muzzle-bag, a soft wad, or a light stopper of wood, suggest themselves as means of security during the interval between loading and firing the gun. The cover or stopper might be removed, or left to be blown away at each discharge.
The longer the interval above alluded to, and the higher the elevation at which the gun is kept, the more important and necessary are these precautions.
396. Much care is taken to give the projectiles uniformity of size; and if the powder is of suitable quality, those now supplied will almost invariably take the grooves. Should difficulty in this respect, however, be experienced, it may be remedied by separating the brass ring from the iron at three or four points of the circumference. This should be done with a cold chisel, very slightly, and so as not to interfere with the loading. It is only necessary to sever the contact of the two metals.
397. As the projectile slides in the gun with very little friction, particularly when greased, the gun should therefore be elevated and eased out when firing to leeward, that the shot may not be started from its seat. An experiment to test this, showed that running a 100-pounder out with the force of its crew against the forward hurter, the gun being level, started the shot forward nearly two feet.
Placing a grommet or other wad over elongated projectiles is positively prohibited.
398. The 100-pounder and 60-pounder guns being, respectively, of the calibres of the 32-pounder and 18-pounder spherical shot, and fired with the same charges, these shot may be fired from them with excellent effect, particularly on ricochet. The round shot should be sewed up in canvas or felt, strapped to a sabot, or snaked between two grommet-wads.
399. Both percussion and time fuzes are supplied for these rifle-guns. When the object to be fired at presents a sufficient resistance, such as masses of timber or earth, ships, or solidly-built houses, the percussion-fuzes alone should be used from rifled cannon. They will, however, frequently fail to explode the shell at long ranges, owing to the shell not striking on its apex; or, if fired into loose earth, which checks its momentum too slowly to make the plunger strike with sufficient force.
400. It has been observed that time-fuzes burn with greater rapidity in shell thrown from rifled cannon. Being in front, they are subjected to greater pressure from the air. A similar effect is produced when the fuze is confined under a water-cap, as in the naval time-fuze.
401. The fuze-holes of the heavy shells are cast larger than the diameter of the regular fuze-stocks of the navy, which can, however, be used with the aid of a bouching or an adapting ring, always sent with the shells.