by the shell in question.

Fig. 27

The tendency of the impact is to stop the rotation of the projectile, owing to the friction between the surfaces in contact, but owing to the length of the projectile the point receives this retarding influence before it can be transmitted throughout the body of the shell to its base. The consequent result is that the head will finally come to a stop while the base is still rotating, however slightly that may be.

Theoretically considering the projectile to be composed of a series of discs a line drawn parallel to the major axis, while at rest, would be represented by the line cd. Upon impact, however, the rotative force tends to create a twisting couple with the result that each disc will tend to slide on its preceding disc, so that by the time these twisting couples have been transmitted to the base of the shell the original line cd will have taken some such position as de.

The objection to the present method of forging shells is as a result, the grain or fibre of the metal lies parallel with the major axis of the forging, the forging process causing an elongation of the ingot and the metal grain following the direction of elongation. Consequently any flaws occurring in the material will extend parallel to the grain or major axis. If a flaw remains undiscovered in a finished projectile—as is sometimes the case—the projectile is not only weakened thereby, but the element of weakness lies in such a direction that the compression forces and counterforces produce very much the same results as would a wedge driven into a niche, i.e. the separation of adjacent material. The author is in possession of a shell in which a longitudinal flaw was revealed in the ogive by the cutting away of a longitudinal quarter section, Fig. 28.