'328 RIFLE ring its flight, the sources of deviation above mentioned will have been removed. No ac- count is here taken of the tendency of the axis of rotation to continue parallel to its origi- nal direction, which (as the path of the ball after it leaves the gun is a curve) gives some deviation from the desired point, as such a discussion involves an abstruse mathematical investigation. If a lead ball be pushed down the bore of a muzzle-loader until it reaches the powder, and then by some means be so expanded that the lead is squeezed into the grooves of the rifling, such a ball will receive in passing through the bore the required mo- tion of rotation. In a breech-loader the lead ball is slightly larger than the bore, and the explosion of the powder upsets it, and forces the lead into the grooves, thus destroying all windage, and giving the necessary motion of rotation about the axis of the bore. Of two balls of the same weight projected from guns, it is evident that that one which presents the smaller surface to the direction of the motion will be less resisted by the air. Hence, other things being equal, the smaller the bore of the gun within practical limits, the less resistance is there to the motion of the ball, or in other words the further the ball will be carried, or technically the flatter will be the trajectory. Formerly the difficulty of loading pieces with small bores prevented the use of small calibres in military arms ; but the general introduction of breech-loaders, in which small calibres can be loaded as easily and quickly as large ones, has caused the advantages of small calibres with cylindrical bullets to be recognized, and the calibres of all breech-loading military small arms manufactured within the past ten years range between '5 in. and -4 in. The great majority range between '45 in. and '4 in. It has been mathematically determined that the larger and denser the projectile, the less in proportion is the resistance of the air. It fol- lows therefore that for the same calibre an oblong projectile is less retarded than a spher- ical one, and that for the same initial velo- city the oblong projectile will have a greater range than the spherical one. It has also been mathematically determined that the length of trajectory of a projectile, in which the ve- locity is reduced by any definite amount, is directly proportional to the product of the diameter and density of the projectile, and inversely proportional to the density of the air. Hence greater ranges are obtained by the use of large and heavy projectiles, in prefer- ence to small and light ones, solid shot instead of shells, lead instead of any lighter metal, and long instead of short projectiles. These prin- ciples have all been applied in the manufac- ture of modern rifled small arms ; but it is only within the past 30 years that the rifle has come into general use as a military weapon. Various styles of rifling have been used in the manufacture of military arms, the differ- ence being in the number and shapes of the grooves and the lengths of the twists. But in general, the grooves are flat, in number from three to seven, and the breadth of the lands less than that of the grooves. In muzzle-load- ers the depth of the grooves diminishes from the breech to the muzzle, but in breech-load- ers that depth is constant. In muzzle-loaders too, as a very great range was not consid- ered attainable, the twist was gentler than it is in breech-loaders. In the former the twist FIQ. 1. Whitworth's Small-arm Projectil6. was generally one turn in 60 in. or more ; in the latter it is usually one turn in 22 in., and in some arms it is a little greater than that. The intensity of the twist is limited by the danger of causing the ball to " strip " in pass- ing through the bore. About 5 per cent, of the force of the powder is taken up in gener- ating the enormous velocity of rotation made necessary to attain the long ranges of modern arms. Whitworth's rifling consisted in ma- king the bore of the barrel hexagonal in sec- tion, with rounded angles, and giving the bore a twist. The effect of this was good, but the difficulty of its manufacture, or rather the ease of manufacture of the cylindrical bore, has caused its general rejection in military small arms. Henry's rifling, which was adopted by the British government for all its small arms, has produced excellent results. Although the section looks as if it might be difficult to bore .01*' Fio. 2. Henry's Rifling. it correctly, yet, on account of the peculiar arrangement of grooves, it is no more diffi- cult to make than ordinary rifling. As small arms became lighter and of more general use in armies, the necessity for a light arm of long range for the use of light troops, sharp- shooters, &c., became more apparent. The fire of the ordinary musket or arquebus was too wild for such troops, and the rifle came gradually into use, but the slowness of its fire
