502 
ARMOUR-PIERCING PROJECTILES. 
Some of these questions have been partially answered by Krupp^s 
experiments. Thus the practice at 1668*9 yds. range has shown that 
the mean error of the shells in a vertical direction is only 18*9 ins. 
The committee think that this accuracy may be considered quite 
satisfactory, because the practice with the 6-in. gun (firing a shell of 
2*8 calibres in length, fitted with bands) gives a mean error in a 
vertical direction varying from 19*8 to 26*4 ins., according to the 
atmospheric conditions. The committee recommend, in addition, 
comparative practice with the naval gun, at ranges between 1093*6 
and 4374*5 yds. 
In order to test the shells of 3*5 calibres in length against armour, 
the committee recommend firing some rounds at a plate with the line 
of fire making an angle up to 25 degrees with the normal. The 
committee think, besides, that in order to place the projectiles thus 
tried under the same conditions, the practice should be against an iron 
plate target with a full charge, and at a range of 109*4 yds. For this 
trial a plate of good quality and a thickness of 8*5 ins. should be used. 
This plate should be perforated by a shell of 112*4 lb., fired at a range 
of 109*4 yds. at an angle of not more than 25 degrees with the normal, 
and with a muzzle velocity of 1679*8 f.s. With direct fire the velocity 
of the projectile fired at the same range of 109*4 yds. should be 
reduced to 1548*6 f.s. 
As recommended by the committee in these trials with oblique fire, 
plates should not be used whose thickness is more or less than 8*5 ins., 
because it is necessary to subject the projectiles to severe trial, and at 
the same time charges not greater than the full charge should be used. 
To lessen the destructive action of the charge on the gun when firing 
such heavy shells, a very dense powder must be used; under these 
conditions, as shown by Krupp’s trials, the pressure at the bottom of 
the bore of a 6-in. gun is about 17*7 tons per square inch, measured 
by the Rodman gauge, a pressure which is not much greater than that 
of 14*45 tons per square inch* as developed in our 6-in. gun with 
service charge and shell of 2*8 calibres in length* One may hope 
that by using a powder sufficiently dense, the pressure on the gun, 
even when firing these heavy shells, will not exceed the limit of 
resistance of the piece, which is laid down as 18*4 tons per square inch 
but as when using such a powder the pressures of the gas in sections 
of the bore, more or less removed from the breech, may acquire a 
greater value then when employing a quick burning powder, which up 
to the present time has been used in this gun, the committee recommend 
that in the ensuing trials the Marine Department should place some 
Rodman gauges in the bore of the 6-in. gun at different distances from 
the bottom of the bore, in order to determine if there be any reason 
to modify the position of the hoops in these new guns* 
These recommendations of the committee have been approved by 
the grand maitre de Vartillerie . 
(“ Bulletin de la Reunion des Offitiers” 6.12. 79., p. 1075$ 
