The Photographic History of The Civil War: in ten volumes, Thousands of Scenes Photographed 1861-65, with Text by many Special Authorities, Volume 5: Forts and Artillery.
Francis Trevelyan Miller, Ed.

Another device consisted of making the projectiles of wrought iron, with the base cup-shaped like the lead bullet for the small arms. There were also systems resembling the Federal Parrott projectiles, and a type that had a sabot like the Schenkl of the Federal service, except that most of the sabots were made of lead. The Whitworth, Hotchkiss, Armstrong, and Blakely types were very effective.

Lieutenant-Colonel J. W. Mallet, who was in charge of the Confederate States Central Laboratory at Macon, Georgia, devised a shell having a polyhedral cavity, instead of a conical or spherical one, in order to provide for a definite number of pieces when it burst. In explanation of his improvement, Colonel Mallet said that it obviously was not a matter of indifference into what number of pieces the shell might separate on bursting; that if the pieces were very small the destructive effect of each would be insignificant, while, on the other hand, if the pieces were large and few in number, the chance of objects in the neighborhood being hit would be slight. With the size of the fragments known, in order to produce a certain effect, it was clearly desirable that the shell should burst into as many pieces of that size as possible, and the fragments should be projected as equally as possible in all directions about the center of explosion. As ordinary shells then made were either spherical or elongated, it was almost impossible to tell along which lines the case would break, since the interior surface was symmetrical and parallel to the exterior. To effect the desired object, Colonel Mallet proposed to cast shells with the polyhedral cavity, so that there would be certain lines of least resistance, along which the shell would be certain to separate.

Prior to the invention of this device, the efforts to cause the shell to burst into equal parts had been confined to the “shrapnel shell” and the “segment shell.” In both of these types the walls of the case were thin, and enclosed a definite number of pieces of metal which would scatter as the shell