-------+----------+----------+-------+--------+-------+---------- | | | | | Muz. | | | | | | Engy. | Calibre|Wt., lbs. | Muz. Vel.| | | Ft. | Type of Inches |Projectile| Ft. Secs.| R.P.S.| R.P.M. | Tons | Gun -------+----------+----------+-------+--------+-------+---------- 6 | | 2,600 | 192 | 15,520 | | | | 3,000 | 222 | 13,320 | | 8 | | 2,200 | 133 | 7,980 | | 10 | | 2,250 | 108 | 6,480 | | 12 | | 2,250 | 90 | 6,400 | | -------+----------+----------+-------+--------+-------+---------- From the above table it will be noted that the R.P.M. are exceedingly high in some cases. Upon the impact of a shell with armor-plate the physical phenomena occur instantaneously and the resultant forces are so great that it is impossible to mechanically record their action. A study of the stresses in the shell can, however, be made on a theoretical basis. In the first place, if the projectile were twenty calibres in length and of a material offering less resistance to torsional stress than steel and rotated at the high velocities indicated we would find that upon impact the torsion would be plainly evident as per the following: Assume a projectile A of length twenty calibres, about to penetrate an armor-plate B of thickness sufficient to prevent complete penetration by the shell in question. [Illustration: 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_.