Let ue now apply these considerations to the action of an ordinary smooth bore gun, whether musket or piece of ordnance.
In order that the shot may be forced down the bore of the gun it must be slightly smaller than the bore, the difference in diameter of the two being called windage. Windage, besides allowing a great escape and waste of gas, causes deflection in two ways, first the ball resting on the bottom of the bore of the gun is forced down by the gas rushing over it at the same time that it is forced along, and bounding up again from its elasticity it is carried along the bore, rebounding from side to side, and eventually leavers it, not in the direction of the axis, but in seine other direction depending on its last impact. Secondly, from this last impact it will carry away a certain rotatory movement, which for the reasons before given will cause it to deflect.
Tho eccentricity of the projectile is another cause of deflection in mouth-bored guns. For the reasons given in the article GUNNEItY, this eccentricity will in the bore of the gun cause rotation, and, as there stated, the effects of this rotation will be the same in nature as those due to the roughness of surface before considered, while they will be greatly augmented. Roughness of surface and imperfection of form are the last causes of deflection, and they are the means by which rotation causes deflection.
Windage may be lessened by increasing the size of the shot and various other insane, but practically it cannot be destroyed, except in breech-loading guns.
Eccentricity, arising from the material of the projectile not being homogeneous, is in musket bullets wholly overcome by making the bullets by compression, instead of casting them, as in cooling a void is often loft in the interior ; and may to a great extent be avoided by care 111 the projectiles used in larger ordnance.
pellets can never be made perfectly smooth. Rotation can never be avoided in smooth-bored guns. It can to a certain extent be taken under control by making the shot purposely eccentric [Gus:Ns:ay], but this is a very uncertain process. We come then to the rifle, in which we
have the power of impressing a certain fixed rotation on the bullet ; a rotation always bearing in velocity a fixed relation to the initial velocity of the bullet. And in direction, a rotation which being round an axis that during the first portion of the trajectory, at all events, Is tangential to it, calms the resistance of the air to be equally distributed round the polo of rotation, and brings any imperfections of surface rapidly round from one aide to the other of the axis, and corrects any deflection arising from them at each half revolution of the bullet. Thus we obtain accuracy in its flight.
According to the laws of rotatory bodies, the tendency is for the axis of rotation always to remain parallel to its original direction. Hence we have the power of using elongated bullets from rifles ; bullets, for instance, of a cylindro-conical form, termed pickets. These being made to rotate on their longer axis, constantly present their points to the resistance of the atmosphere, and at the same time hat they present an area of resistance of the same size as a spherical sullet of the same diameter, they possess, supposing them to start vith the same initial velocity, a much greater momentum to overcome his resistance. Therefore, the retardation being less [Gusaenv], we )btain a greatly increased range. A cylindro-conical picket cannot be Ire] from an ordinary smooth-bored gun, because, assuming a rotation dmost immediately on leaving the muzzle round some of the shorter saes, all advantage is lost.
The tendency of all rotating bodies to rotate round the shortest axis of greatest momenta is an important consideration in the con gruction of rifle pickets. If the cylinder be very long and solid, tho tendency is for the bullet to upset during its flight. The hollow at the base of most rifle pickets is therefore of great assistance in retaining the impressed rotation. There are two other points connected with the rotation of the picket, which it may be as well to notice before proceeding to the description of the rifle itself.