1st. The action of a rifle being the same as that of a nut on a screw driven through it, the action of the powder on a bullet in a rifle barrel must be the same as that of a pressure moving a body np an inclined plane, the direction of the pressure being parallel to the base. The greater the inclination of the plane, the lean the velocity in the direction of the pressure generated in the body in its passage over a given space in the same direction, because of the greater inclination of the plane, and also because of its thereby increased friction.
In the rifle, therefore, the greater the inclination • of the grooves, the less will be the initial velocity due to a given charge. Hence the inclination of the grooves should be the least that will effect the purpose ; that is, that will give the bullet sufficient rotation round its axis to retain it parallel to its original direction during its flight This inclination, as given in Straith's Artillery,' by Cook and Hyde, is With respect to the form to be given to the grooves in section, and their number, it. is evident that the main consideration on which they depend is the manner in which the projectile takes its rifling. If it. is by the expansion produced by the explosion, it. is evident that they should be wide and shallow, rounded and not angular, while the groove or furrow on one side is opposite the projection or land on the other side. The Enfield rifle, described further on, with its three wide, shallow, rounded grooves, fulfils these conditions. If on the other hand the projectile takes its rifling by being forced into a narrower bore, as in the breech-loaders, it is evident that the cutting portions, the lands, should be narrow, the grooves not very deep, not deeper than will just. suffice to give a sufficient hold, with sharp angles and square sides at least on one side. The Armstrong gun [RIFLED ORDNANCE], with its numerous narrow lands and furrows, is made in this way.
If the projectile is formed to fit the grooves for convenience in load ing, they and the projections on the projectile to fit them should be made prominent and well marked, as in the two-grooved rifled Jacob's or AVhitworth's. This last mentioned form, however, is also well adapted for an expanding ball, and while it gives a perfect hold on the projectile reduces friction to a minimum.
2nd. The picket should be as long in proportion to its diameter as possible; for, ca feria paribus, the longer and thinner the projectile is, the greater will be its range and accuracy. But at the same time it
must be remembered that, first, especially for military rifles, there are great objections to a verysmall bore and attenuated picket : the former being difficult to clean, the latter liable to injury, and requiring a long fragile cartridge. Secondly, the inclination of the grooves is necessarily Increased, in order to give the picket sufficient rotation ; which, besides being objectionable for the reasons before given, renders the bullet liable to strip, especially with the soft metal required in expanding bullets. Thirdly, the bore may be so diminished as to prevent the power of giving the picket sufficient initial velocity ; that is to say, that, given the calibre, there is a limit beyond which it is detrimental to increase the length and consequent weight of the projectile, on account of the mechanical distribution of the charge.
3rd. There are certain mechanical considerations : among which are a barrel of sufficient weight, perfectly true bore, with accurately parallel grooves brought to a high state of smoothness ; and, when the rifling is taken by an expanding bullet, the distribution and depth of the grooves such as will allow of their being perfectly filled. Three wido shallow grooves appear the best, as in the Enfield rifle. Rifles with ;minim!' laid., that in, a spiral increasing in inclination from breech' to muzzle, have been tried. In fact the Lancaster rifles, with which the Royal Engineers are armed, are of this description ; these have made good practice, but it may be only from superior manu facture, fur it is evident that there is nothing gained, hut, on tho other hand, when the projectile is long, there is a constant alteration of form, causing increased resistance. These various points require a long series of carefully conducted experiments to arrive at any absolute rules.
Commencing with the greatest weight of bullet, on account of recoil, , that it is possible for a man to fire from his shoulder, and investigating how far the greatest advantage in each direction may be obtained, compatibly with the conflicting considerations, is the only manner in which a perfect rifle can be formed. We believe that this is the manner in which Mr. Whitworth arrived at his proportions, and his is certainly the most perfect weapon yet produced.