ARMOUR-PIERCING PROJECTILES. 
485 
against iron, was inferior to a 1*5 diameter head when fired obliquely; 
and was not superior to a 2*0 diameter head when fired obliquely at a 
steel-faced plate. 
On the whole a 2*0 diameter head gave the best results, especially 
with chilled shells. The limited trials with the heads of 2*5 and 3*0 
diameters only showed that these were inferior to the 2*0 diameter 
head when fired obliquely at iron. 
The Committee turned their attention to the best weight for an 
armour-piercing projectile in terms of its diameter. 
Obviously, the weight is some function of the diameter, or W = f(d)» 
Suppose W = ad z , where W is the weight in pounds, and d the 
diameter of the projectile in inches, a being a constant. 
W must vary as the cube of the diameter, for taking the projectile 
for the sake of simplicity to be a solid cylinder of density, I>, then 
and 
7J , 77^2 D x 1000 
W= — l Dl , where D x = 18xm8 ! 
l = length of cylinder in inches ; 
but l also depends on the calibre of gun, remembering that the maxi¬ 
mum of l depends on the twist of the rifling expressed in calibres. 
Hence l oc d 3 or l — bd , where b may vary between 2 and a superior 
limit, usually not exceeding 3*5, depending on the twist of the 
rifling. 
,r/-72 
Therefore, W =-- x bd x A ; 
3 4 
or if 
W= ad 3 . 
The Committee thought that the value of a was somewhere beyond 
0*364, but this seems hardly borne out by the tables cited, in the 
sense that this value of a seems somewhat low: perhaps on the whole 
a — 0*400 would seem to be a better value for a low limit. 
The respective advantages of heavy and light shells may be said to 
be as follows, assuming the powder charge to be constant:— 
The heavier shell, though starting with a lower M.Y., keep up their 
velocity better than the lighter ones, and so have a longer range of 
penetrative effect. 
The lighter shell have a higher velocity at short ranges and a flatter 
trajectory, also a great number of projectiles can be carried for a given 
weight. This last advantage, however, lies in very narrow limits.* 
* These are only the main considerations, there are various minor ones, and to attempt to lay 
down a hard and fast line for the value of “3 would, with our present knowledge, be presumptuous. 
To go into the matter thoroughly would require a separate paper. 
60 
