498 
ARMOUR-PIERCING PROJECTILES. 
6 -in. guns; for this reason it asked the advice of the artillery committee 
as to the most suitable parabolic trace for a 6-in. gun intended to fire 
a shell 4 calibres in length; also, the section asked, if the artillery 
committee did not consider the parabolic trace for the grooves is the 
most convenient for manufacture, and is that actually in use at the 
Oboukhoff foundry; there being great difficulty in the preparation of 
new directrices required for each change in the inclination of the 
grooves. Concerning the length of bore, the depth and number of 
grooves, the artillery section proposed to hold to the data communicated 
as to the Krupp 6-in. gun, viz., length of bore, 25*4 calibres, number 
of grooves, 37, depth of grooves, 0*197 ins. 
They propose to determine the dimensions of the powder chamber 
for a charge of 37*46 lb. prismatic powder, having a density of 1*75 
(23*6 cubic ins. per lb.) placed in layers of 12 prisms; besides 410 
grammes of powder should correspond to 0*528 cub. dec. of the volume 
of the same chamber, and the length of the chamber for the projectile 
would be fixed according to the length of a shell of 4 calibres. The 
form of the shells of cast-iron, chilled iron, or of steel would be 
calculated so that the weight of each should not exceed 112*9 lb. 
After an examination of this statement, the artillery committee gave 
the following opinion :— 
The increase in weight of the projectile, and of its muzzle velocity, 
much augments the destructive power of a gun of given calibre. 
Trials were made in England during the autumn of 1878 with two 
Armstrong guns, one of 6-ins. and the other of 8-ins. calibre, weighing 
respectively, 3*228 tons and 11*28 tons, and giving to the projectiles 
of 79*366 lb. and of 180*779 lb. muzzle velocities of 2001*3 f.s. and 
2099*8 f.s. 
In spite of these great muzzle velocities, the pressures did not exceed 
9*85 tons per square inch in the bore of the 6-in. gun, and 11*15 tons 
per square inch in the 8-in. gun; but, so far as can be judged, the 
method of measuring these pressures in England (viz., by crusher 
gauges) gave, as showed by comparative trials in France, pressures 
much lower than those recorded by the Rodman gauge. By obtaining 
such muzzle velocities as the above, the destructive effect of the 
projectiles is so increased that the new 6-in. gun perforates at short 
ranges plates of the same thickness as those pierced by the English 
service 9-in. gun; whilst the new Armstrong 8-in. gun perforates 
plates of the same thickness as are pierced by the English service 
12 -in. gun. Thus the increase of muzzle velocity of the projectile 
renders it possible to pierce, at a short range, with a 6-in. shell the 
same plate which a 9-in. shell perforates, having a length of 2*4 calibres 
and a muzzle velocity of about 1410*8 f.s. 
Considering that the velocity of a projectile can possibly be 
maintained at different distances by increasing its weight in proportion 
to each unit of surface of transverse section, Krupp tried, at the 
beginning of the year, two 6-in. guns, of which one fired (like the 
Armstrong gun) shells of the usual length with a muzzle velocity of 
2132*6 f.s., and the other is intended to fire long shells with a muzzle 
velocity of 1673*3 f.s. The long shells of cast-iron are 4 calibres in 
