500 
ARMOUR-PIERCING PROJECTILES. 
Armstrong, as we have seen above, has not tried in bis experiments 
a shell of increased weight, and he has obtained, by increasing the 
velocity, similar results to those obtained by Krupp with a shell which 
was not lengthened. 
By increasing the weight of shell from 69*1 lb. to 111*1 lb., and 
preserving the same muzzle velocity of 1679*8 f.s., the thickness of 
plate perforated is increased Jrdby direct fire at a range of 2332*7 yds., 
as well as at a range of 1632*8 yds. It is shown by this table that 
for a given calibre, one derives more advantage as to the perforating 
power of the projectile by increasing its weight, than by augmenting 
its muzzle velocity; indeed, the increase of thickness in plate perforated 
by the heavier projectile is -Ath at a range of 1632*8 yds., and £th at 
at a range of 2332*7 yds., compared with the perforation of a projectile 
of the ordinary weight fired with a greater muzzle velocity. 
The increase in weight of shell, as tried by Krupp, diminished to 
such a degree its loss of energy at long ranges, that with direct fire 
with these projectiles one would expect the perforating power to be 
much greater when compared with that of shells of the ordinary length. 
Thus, always considering the fire to be direct, the 6-in. gun firing a 
shell of 3*5 calibres could perforate, at a range of 2332*7 yds., the 
same plate that could be perforated by a 7* 7-in. gun, made after the 
pattern of our coast guns of 1877 ; the 6-in. gun firing, on the other 
hand, a shell of the ordinary length, but with increased velocity, would 
pierce at a range of 2332*7 yds. the same plate that could be perforated 
by a 6*693 in. gun made after the pattern of our coast guns of 1877. 
It must be remarked that these guns of 7*7-in. and 6*693-in. calibre 
would weigh much more than the 6-in. gun of Krupp. 
Considering the advantage that there would be for a gun of a given 
calibre in having an increase in the weight of the shell, whilst preserving 
a sufficient muzzle velocity, the artillery committee thought that it 
would be very useful, as proposed by the artillery section of the 
marine committee, to test 6-in. shells (cast-iron 4 calibres, and steel 
3 calibres in length) which should be fired from a 6*in. hooped 
steel gun. 
According to the wishes of the section, the committee have decided 
on the form of a 6-in. shell of 4 calibres in length, as well as that of 
the bore and chamber of the gun, from which it is proposed to fire 
them. The rifling has been calculated so that at the muzzle it has an 
inclination of 1 in 25 calibres, the pressure on the projectile in the 
chamber would be about equal to the pressure towards the muzzle. 
The inclination of the rifling at the breech, calculated on this condition, 
has been found to be 3° 12'. 
The development of the rifling on a plane surface is parabolic; this 
form is chosen because it could be easily obtained, without the help of 
a special guide, by means of two uniform rectilinear movements in 
two directions perpendicular to each other. After trials at the Perm 
foundry, this is the principle on which the rifling of our guns of 
pattern 1877 have been made. This will render useless the employ¬ 
ment of templets, the form of which must change with the nature of 
the gun and the inclination of the rifling, and, besides replacing the 
