Be it known that I, CARLOS DE ZAFRA, a citizen of the United States, residing at New York city, county of New York, and State of New York, have invented certain new and useful Improvements in Projectiles, of which the following is a specification. My invention, relates to an improved form of explosive shell or other projectile, and more particularly to those projectiles which are reinforced by longitudinal ribs. It further relates to a method whereby such a projectile may be made. The object of my invention is to provide a shell having a maximum strength or perforating power, together with a maximum capacity for an explosive charge, and the invention consists in forming the projectile with the fibers or grain of the metal running in a spiral direction from the base of the shell to the top thereof, and in reinforcing the interior of the shell with ribs which shall run in the same direction, starting at the base of the projectile and ending at the top end of the inner chamber. In the drawings, Figure 1 is a side view of a projectile, the grain or fiber of which is indicated by dotted lines. Fig. 2 is a longitudinal section showing the interior ribs. Fig. 3 is a transverse section on the line 3--3, Fig. 2. While the tendency to rupture is very much lessened by the use of straight longitudinal ribs on the interior of shells and projectiles of various kinds, yet such a straight longitudinal rib is itself liable to a sheering and disruptive stress along transverse lines when the projectile strikes, due to the rotative inertia of the projectile in its flight. The aim of my invention is to provide ribs which will be coincident with the rotative travel of the shell so that when the point of the projectile enters an armor plate, the stress of this sudden stoppage of rotation will be taken up along the fiber or grain of the shell and by the spiral ribs therein. Thus the sheering tendency of the metal in the walls of the shell is greatly reduced and greater strength is given to resist the tendency of the rear end of the shell to twist off, due to the rotatory course when the head of the shell is embedded in an armor plate. Like letters in the figures designate like parts. A represents the shell, and B the fuse, B' being the rotating band which is secured on the shell near the base in the usual way. The hollow portion of the shell consists of a chamber C extending from the base to the forward end of the shell. The walls of this chamber are provided with the ribs D extending from the base to the point of the chamber in a spiral direction. In the drawings, I have shown the pitch of this spiral as one quarter turn in the length of the chamber, but it is to be understood that I may use a greater or less pitch without departing in any way from my invention. I have shown a pitch of one quarter turn particularly for purposes of illustration, as if a greater pitch had been used the section Fig. 2 would not have shown any one rib entirely.