314 THE SPORTING RIFLE. 



spending manner. Both modes are adopted by different 

 makers, but in the machine shown in figs. 66 and 67, the plate 

 is made to revolve, and each of the circles shown upon it is 

 divided accurately into either two, three, four, five, six, seven, 

 eight, or nine equal sections, so that if a barrel is to be cut 

 with three grooves, the circle with three equal divisions is 

 used, and the plate being moved in exact correspondence 

 with them, the work is beautifully correct. So also the 

 shape of the cutter determines the form of the groove, being 

 nearly semicircular for the oval bore of Mr. Lancaster, as 

 shown in the engraving illustrating Captain Beaufoy's cele- 

 brated work, " Scloppetaria." Again, for a groove with sharp 

 angles, the cutter is made correspondingly sharp, for as it 

 traverses backwards and forwards, it leaves its mark exactly 

 of its own shape, allowing for the slight vibration inseparable 

 from the working of a rod confined at one end only. 



The principle, therefore, upon which all rifle grooves are 

 made is the same, though in the next chapter the variation 

 will be shown to be immense in the modes by which that 

 principle is applied. 



TECHNICAL TERMS. 



One of the most important defects in a rifle is, the existence 

 of such a space between the ball and the sides of the barrel, 

 or of its grooves, as to allow of an escape of gas generated 

 by the explosion of the powder. This, of course, is attended 

 with a corresponding loss of power, and is known among 

 rifle makers and shooters by the term " Windage" I have 

 already, at p. 306, given a definition of "upsetting;" but 

 there are three terms constantly used in rifle shooting which 

 require some notice here. These are 1st, " The line of fire;" 

 2nd, " The aim ;" and 3rd, " The trajectory." The line of 

 fire is the indefinite projection of the axis of the barrel. The 

 aim is a straight line drawn from the centre of the back 

 sight to the top of the front one, and prolonged to the object 

 at which the rifle is directed. Lastly, the trajectory is the 

 curve actually described by the ball in its passage through 

 the air, and greater or less in proportion to its velocity. 



