(c) 12-inch deck piercing shell. Two shell, sandfilled to standard weight, will be fired with a striking velocity sufficient to pass completely through a 4½-inch nickel-steel protective-deck plate inclined so as to give an angle of impact of 60 degrees, and to be supported by a suitable backing of wood; or both shell shall be subjected to such alternate ballistic test as the Department may judge to be an equivalent to the above in its effect upon the projectile.
The nickel-steel protective-deck plate shall be manufactured by the open-hearth process and shall contain about 3¼ per cent of nickel, not more than six one-hundredths of one per cent of phosphorous; not more than four one-hundredths of one per cent of sulphur, shall be the best composition in all respects.
It shall be oil or water tempered and annealed, and the whole plate shall be subjected to the same treatment at the same time.
Tensile test will be made after final treatment. One longitudinal specimen for tensile test will be taken from each plate. Each shall show a tensile strength of at least 80,000 pounds per square inch and an elongation in 2 inches of at least 27 per cent.
Bending tests will be made as follows: A piece cut from the plate shall be doubled cold around a curve of which the diameter is not more than the thickness of the piece tested without showing any cracks. The ends of the piece are to be parallel after bending. These specimens shall be 12 inches long, 1½ inches wide, and 1 inch thick.
At the discretion of the inspector, bending specimens ½ inch square taken with a hollow drill, may be substituted. Such specimens must bend cold to 180 degrees flat, without sign of fracture on outer surface.
(d) 12-inch Torpedo Shell. Two shell, sandloaded to standard weight, will be fired from a gun or mortar into a sand butt with a pressure in the powder chamber of about 37,000 pounds per square inch to test structural ability.
If the shell are found not seriously deformed by discharge from the piece and in a condition for effective bursting, the lot will be accepted.