Manufacture of Projectiles

While a high state of development has been attained in the manufacture of armor-piercing shells attention will be confined to their manufacture in so much as the methods for improvement hereinafter suggested are intended to affect the physical and not the chemical properties of the material, and are, therefore, applicable to all projectiles in which the stresses to be resisted exceed the resisting powers of the projectiles as at present manufactured.

The function to be performed by an armor-piercing shell is that of fully penetrating, without disruption to itself, an armor plate in thickness equal to, at least, the calibre of the shell in question, and then be in condition for effective bursting.

The following extracts from the Army and Navy specifications pertain to:

Material and Workmanship

(Art 20, O. D., U.S.A.)

The projectiles must be of forged steel, sound, and free from cracks, seams, and other defects 1.

The base plugs must be of forged steel, annealed after forging or tempering, free from seams, cracks, and other defects, and have the following physical properties:

The projectiles shall be machine-finished, before treatment, as close to the prescribed dimensions as may be consistent with that operation, and must, if necessary, be finally finished to the prescribed dimensions within the allowed variations.

Cylindrical tensile-test specimens with diameter of stem of 0.505 inch will be used in all cases when the piece is sufficiently thick to finish the stem to that dimension; when not, the inspectors will determine the exact form or diameter of the specimens to be used, the largest practicable being used, considering the piece under test. A length of stem between gauge marks of 2 inches will be used in all cases where the elongation is to be taken.

1 Italics are those of the author and refer to defects which it is the object of his design and method of manufacture to remedy.

Capping

(Art. 21, O. D., U.S.A.)

All steel projectiles shall be fitted, when required, with a cap of soft steel placed upon the point, 2 the caps to be of the dimensions shown on the approved drawings and secured in a manner satisfactory to the Chief of Ordnance by means of a groove, to be turned on the head of the projectile prior to tempering.

The steel for the cap must show a tensile strength not to exceed 60,000 pounds per square inch, an elongation after rupture of not less than 30 per cent, and a reduction in area of not less than 45 per cent on standard specimens, 2 inches long between measuring points and 0.505 inch in diameter. These caps will be thoroughly annealed before being placed upon the projectiles and will be free from cracks and all other defects.

2 See Frontispiece.

Test for Detection of Holes, Cracks, Etc.

(Art. 27, O. D., U.S.A.)

After the submission of a lot to the inspector for selection of samples for ballistic test, and before final delivery, the projectiles must be subjected to an interior hydraulic pressure of 500 pounds per square inch for one minute. All projectiles in which holes, cracks, or any unsoundness are developed by this test will be rejected.

Tensile Test

(Art. 28, O. D., U.S.A.)

After forging, the projectiles shall be annealed at a temperature of at least 1,200° F.; and after being annealed, tangential test specimens shall be taken from the base or base prolonged of 2 per cent of the projectiles from each lot selected at random by the inspector.

The tensile strength of the projectiles in a lot shall not vary more than 20,000 pounds from the highest to the lowest.

Chemical Test

(Art. 30, O. D., U.S.A.)

A careful and complete chemical analysis shall be made of the metal of each heat from which the projectiles are manufactured under these specifications.

Tests for the Detection of Initial Strains Bordering on Rupture

(Art. 31, O. D., U.S.A.)

After final treatment and before acceptance for the ballistic test, all A.P. shot must be cooled to a temperature of about 40° F., and then suddenly heated by being plunged into a bath of water at a temperature of from 180° F. to 212° F., as the Chief of Ordnance may direct. When thoroughly heated to this temperature each projectile must be plunged, with its axis horizontal, halfway into a bath of water at a temperature not greater than 40° F., and after a brief period shall be turned 180° for a like immersion of the opposite side, after which the projectile shall be removed from the bath.

This test shall be made in the presence of the inspector, and an interval of at least three days must elapse between the final treatment and the submission of the projectiles to this test. This test is not required for shell.

Ballistic Test

(Art. 32, O. D., U.S.A.)

Each lot of projectiles shall be subjected to the following ballistic test:

After a final treatment and on presentation of the entire lot for the ballistic test, the inspector shall select three projectiles to represent the lot, which shall be finished, inspected and delivered in the same manner as required for the rest of the lot.

(a) Armor-piercing shot. Two capped shot, sandloaded to standard weight, shall be fired against a hard-faced Krupp armor plate from 1 to 1½ calibres thick, secured to a timber backing in a manner satisfactory to the Chief of Ordnance, with about the corresponding velocity given by the following table, with the requirement that the shot shall perforate the plate unbroken and then be in condition for effective bursting.

If both projectiles fulfill the above test, the lot will be accepted.

If, one of the shots fails to pass the test here