ARMOUR-PIERCING PROJECTILES. 
501 
rectilinear directrices when worn out, is much more easy than in the 
case of these templets ; lastly, it establishes one principle for different 
natures of guns and inclination of rifling; indeed it settles in a 
convenient manner the connection between the speeds belonging to the 
two perpendicular directrices and the position of the fixed point in the 
rotation of the cutter. The chamber of the proposed gun is made like 
that of the 6-in. gun tried by Krupp. Besides., in order to lessen the 
destructive effect of the charge, this chamber has been given 0*984 ins. 
more than the proportional length of the Krupp chamber. The 
diameter of the chamber is 0*748 ins. more than in the 6-in. gun of 
pattern of 1877. 
The Oboukhoff foundry must, in order to introduce the tube, increase 
much the diameter of the prolongation of the bore to the rear of the 
wedge, and in order to prevent strain of the wedge when firing, it 
will be necessary to screw a screwed cylinder in this prolongation of 
the bore, similar to that in the Oboukhoff field guns. 
The charge of prismatic powder (of usual form), by the recommenda* 
tion of the committee, is to be determined so as to give a cast-iron 
shell of 4 calibres in length, a muzzle velocity of 1679*8 f.s. The 
same charge is to be used for the steel shell of 3*5 calibres. 
To determine the pressure, two Rodman gauges must be placed in 
the wedge. The drawing of the 4 calibre shell shows the interior ribs 
like that of the double shells of the English artillery, in order to 
prevent premature explosions in the bore of the gun. The weight of 
these shells filled is about 112*4 lb., and the weight of the bursting 
charge is 6*7 lb. 
As these ribs diminish considerably the capacity of the shell, the 
committee think it will be well to try at the same time some shells 
with ribs, and others without ribs, but the latter to have their walls 
rather stronger than as shown in the drawing. If these shells without 
ribs do not break up in the bore, a bursting charge of 8*1 lb. could 
be used. The size of the rear band has been shown on the drawing, 
so that the pressure on the driving side of the groove, per unit of 
surface, will be precisely the same as with the service 6-in. shells fired 
with a charge of 19*8 lb. of prismatic powder of 1*68 density. 
In the experiments which the Marine Department propose to carry 
out with this 6-in. gun, the committee think that it will be well to 
investigate, as far as possible, the following questions :— 
1. Are the shells of 4 calibres in length sufficiently accurate at 
different ranges ? 
2. In what degree is the efficiency of the 3*5 calibre steel shells 
reduced in oblique fire, comparing them with the present service 
shells ? 
3. Can special steps not be taken to lessen the redaction of the 
gun on the carriage, and to diminish the recoil ? 
