As will be seen by Fig. 1, the grain or fiber of the metal is also twisted spirally in accordance with the pitch of the ribs D, in this case a quarter turn from the rear end of the projectile to its point. In order to manufacture a projectile of this character I have devised the following method which I deem preferable, though I do not wish to limit myself thereto. This consists first in casting an ingot from which the solid forging is to be produced. Previous to, during or after the process of forging, the ingot is twisted in a torsion apparatus, one end of the ingot being held fixed while the other end is being rotated by any suitable rotative gripping mechanism through an arc of the number of degrees desired. This will result in what I term a "twist forging" in which the grain or fiber will lie in any predetermined or desired spiral direction or pitch. The spiral ribs which are to lie in the direction preferably parallel to the grain or fiber of the metal may now be formed by the boring process similar to that employed in the rifling of modern artillery. My projectile might also be formed by forming the shell with the ribs running longitudinally there along in a direct line from front to rear and with the fiber of the metal also running in a direct line parallel with the ribs. The projectile might then be reheated for forging and while being forged the rear could be held in any suitable gripping device and the forward end be rotated, as before explained. Thus the fiber of the shell and the interior ribs will both be given the spiral twist desired. It will be seen that with either of these processes the fiber of the shell and the spiral ribs lie parallel to each other and are most perfectly formed to resist the shock of impact, the reaction of which will be along the line coincident with the resultant of the angular or rotative and the trajectoral velocities, which line will lie parallel with the spiral ribs, the pitch of such fiber and ribs having been predetermined by suitable calculation. The above described methods while not claimed herein are to form the subject-matter of a separate application. Having described my invention what I claim is: 1. A projectile provided with a chamber extending along its length, the walls of said chamber being provided with longitudinal ribs extending in a spiral direction from the base of the chamber to the forward end thereof. 2. A projectile provided with a chamber extending along its length, the forward end of said chamber being pointed, the walls of said chamber being provided with longitudinal ribs extending in a spiral direction from the base of the chamber to the point thereof. 3. A projectile having the fibers of its material twisted in a spiral direction from the base of said projectile to the end thereof.