4. A projectile having the fibers of its material twisted in a spiral direction from the base of said projectile to the end thereof, said projectile having a central chamber, the walls of which are provided with longitudinal ribs extending in a spiral direction from the base of the chamber to the point thereof. In testimony whereof, I have signed my name to this specification in the presence of two subscribing witnesses, this sixth day of December, 1906. CARLOS DE ZAFRA. Witnesses: EMILO BELARI, EMMA RODERICK. Bibliography ORDNANCE AND GUNNERY BRUFF TEST BOOK OF ORDNANCE AND GUNNERY INGERSOLL REPORT ON THE ART OF WAR IN EUROPE--1854-1855-1856 COL. R. DELAFIELD, U.S.A. JOURNAL OF THE U.S. ARTILLERY THE SCIENTIFIC AMERICAN SPECIFICATIONS OF THE BUREAU OF ORDNANCE, U.S. NAVY DEPARTMENT SPECIFICATIONS OF THE ORDNANCE DEPARTMENT, U.S. ARMY [Illustration: The de Zafra Improved Armor-Piercing Shell]