THE DEVELOPMENT OF ARMOUR. 
558 
m mm 
case of some secret 
process, when accep¬ 
tance depends entirely 
on ballistic tests. 
The Government 
furnish copper bands 
and gas checks. Ar¬ 
mour-piercing projec¬ 
tiles are specified to be 
of forged and harden¬ 
ed steel, annealed at 
least 1200° Fah. after 
forging. Inspectors 
follow the projectile 
through each stage of 
manufacture. Before 
acceptance for ballistic 
trial, projectiles are 
^tested for “ initial 
strains bordering on 
rupture,” by being 
brought to 40° Fah., 
plunged into water at 
The interior of 
to 
Fig. 28. 
from 180° to 212° Fah., and then again at 40° Fah. 
the projectile is also subjected to a hydraulic pressure of 500 lbs. 
the square inch, and the development of holes, cracks, or unsoundness 
causes rejection. 
For the ballistic test of armour-piercing shot, two projectiles are 
fired normally at 1,500 ft.-secs, velocity at a steel plate whose thick¬ 
ness is one and one-eighth times the calibre of the shot. If two 
out of three shots pass through plate and wood backing, without 
cracks or deformation, the lot is accepted. The Government reserve 
the right to make the following alternative test, namely, that two out 
of three shots shall pass through a hardened-faced plate one calibre 
thick, either whole or in fragments ; the striking velocity to be 
about 1,900 ft.-secs. Armour-piercing shell are fired against a nickel- 
steel, oil-tempered and annealed armour plate 44-in. thick for 8-in., 
and 5f-in. for 10-in., and 7-in for 12-inch shells. With a striking 
velocity of about 900 ft.-secs. two out of three shells must pass 
through without being broken or materially deformed. 
The importance of securing that the metal of projectiles is in a normal 
and not in a strained condition was brought out by the discovery, 
these three 4-in. A.P. shells had exploded in store in Devonport. a.p. sheila 
That is to say the shells were found in fragments and the powder burst in 
exploded, but the fragments were so little moved from their orginal 
position and so little harm was done that it was concluded that the 
shells had not been burst by their charges and had broken from 
spontaneous molecular action and that sufficient heat had been gen¬ 
erated to burn the powder after rupture had begun. The explosion 
store. 
