Page:Miscellaneous Papers on Mechanical Subjects.djvu/84

74 the breech to the muzzle may receive a rotatory combined with a forward motion.

The system of rifling by grooves is the one that has been generally employed, and many experiments with different numbers of grooves, some of varying depths being deeper at the breech, and with different turns, some increasing towards the muzzle, have been tried and thought advantageous at various times.

The Enfield rifle has three grooves, with a pitch of 6 feet 6 inches, so that the bullet receives half a turn round its axis while moving through the barrel, the length of which is 3 feet 3 inches. The bullet, as is well known, is cylindro-conoidal, it is wrapped in paper and made of such a diameter as to pass easily down the barrel. It requires very pure lead to allow of its being properly expanded or "upset," by the explosion, and is driven partly against the original portions of the bore, called the lands, and partly in the form of raised ribs is forced into the grooves, whose spiral shape gives the required rotation. See figure A.

In the system of rifling which I have adopted the interior of the barrel is hexagonal, and, instead of consisting partly of non-effective lands and partly of grooves, consists of effective rifling surfaces. The angular corners of the hexagon are always rounded, as shewn