RIFLE, a fire-arm, which has the inside of its barrel cut with from three to nin or ten spiral grooves, so as to make it re semble a feinale screw, varying from a common screw only in this, that its grooves-or rifles are less deflected, and approach more to a right line ; it being now usual for the grooves with which the best rifled barrels are cut, to take about one whole turn in a length of thirty inch es. The number cf these grooves differ according to the size of the barrel, and fancy of the workman ; and their depth and width are not regulated by any inva riable rule. The method of loading them is as follows : when the proper quantity of powder (one drachm avoirdupois) is put down at the muzzle, and a piece of calico or linen is gently rammed down over it as a wad, a circular piece of strong calico is greased on one side, and laid on the mouth of the piece, with the greased side downwards; and a bullet ofthe same size as the bore of the piece before the grooves were cut, being placed upon it, is then forced gently down the barrel with it ; by which means, the calico in closes the lower half of the bullet ; and, by its interposition between the bullet and the grooves, prevents the lead from being cut by them, and, by means of the grease, slides down, without its being ne cessary to use any violent efforts, which would destroy the circular shape of the bullet. In order to understand the cause of the superiority of a rifle-barrel gun over one with a smooth barrel, it will be necessary to refer to Mr. Robin's disco very of the cause of the irregularities which occur in the flight of projectiles from smooth barrels, which we shall give in his own words, " Tracts on Gunnery," p. 196, &c. " Almost every projectile, besides the forces we have hitherto con sidered, namely, its gravitation, and that resistance of the air which directly oppos es its motion, is affected by a third force which acts obliquely to its motion, and in a variable direction ; and which, conse quently, deflects the projectile from its regular track, and from the vertical plane in which it began to move ; impelling it sometimes to one and sometimes to the other, occasioning thereby very great inequalities in the repeated ranges of the same piece, though each time loaded and pointed in the same manner ; and this force, operating thus irregularly, I con ceive to he the principal source of all that uncertainty and confusion in the art of gunner), which bath hitherto been usual ly ascribed to the difference of powder.
The reality of this force, and the cause which produces it, will, 1 hope, appear from the following considerations : It will easily be granted, I suppose, that no bullet can be discharged from the pieces generally in use, without rubbing against their sides, and thereby acquiring a whirl ing motion, as well as a progressive one ; and as this whirl Will, in one part of its re Volution, conspire in some degree with the progressive motion, and in another part be equally opposed to it, the resist ance of the air on the fore-part of the bul let will be hereby affected, and will he in creasedin that part where the whirling mo tion conspires with the progressive, and diminished where it is opposed to it. And, by this means the whole effort of the re sistance, instead of being in a direction opposite to the direction of the body, will become oblique thereto, and will pro duce those effects already mentioned. If it were possible to predict the position of the axis, round which the bullet should whirl, and if that axis were unchangeable during the whole flight of the bullet, then the aberration of the bullet, by this ob lique force, would be in a given direction, and the incurvation produced thereby, would regularly extend the same way, from one end of its track to the other. For instance, if the axis of the whirl were perpendicular to the horizon, then the deflection would be to the right or left; if that axis were horizontal, and perpen dicular to the direction of the bullet, then the deflection would he upwards or down wards. But as the first position of this axis is uncertain, and as it may perpetu ally shift in the course of the bullet's flight, the deviation of the bullet is not ne cessarily in one certain direction, nor tending to the same side in one part of its track that it does in another ; but it more usually is continually changing the ten dency of its deflection, as the axis round which it whirls must frequently shift its position to the progressive motion by ma ny inevitable accidents."