THE ROYAL ARTILLERY INSTITUTION. 
491 
its rifling and tlie fit of the projectile. Yon will recollect that I men¬ 
tioned that the cast-iron of the projectile should not come in contact 
with the gun-metal of the bore. The depth of the groove of the 
Indian gun is iVoths of an inch, and the projection of the studs is 
T a o 3 oths; deducting one from the other, we have a clearance of f |-Qths of 
an inch between cast-iron and bronze.* Up to about 2500 rounds fired 
from one gun tried by the Indian Committee, the impressions show 
that there has never been any contact between the hard and the soft 
metal. When, however, the grooves at the seat of the shell have been 
burnt out by the powder to such a depth that the top of the stud can 
no longer touch the bottom of the groove before the projectile is 
centred, then, of course, contact takes place between cast-iron and 
bronze, and the gun soon becomes unserviceable.f 
Before a single round was fired, I convinced myself that what was 
clear in the afore-mentioned figures as to the isolation of the cast-iron 
from the bronze, was carried out in fact. A lamp was put into the 
bore, and then a shell. On looking into the bore, I saw a circle of light 
all round the shell, saving where it was interrupted by the studs. I 
knew then that all was clear. The drawing will give you some idea of 
the appearance.f 
As to the centering. Supposing you are watching a railway train 
going away from you along a line of rails perfectly straight for a certain 
distance, and then curving away to the right. The most ordinary 
observation or thought would convince you that when the train comes 
to the curve, the flanges of the near or left wheels will rub against the 
inner edge of the rail they run on; thus the near rail will divert or drive 
the train to the off side. 
Now, turning to guns, suppose you cut the breech off a rifled gun, so 
as to be able to look through the bore,J that the rifling has a right- 
handed twist, and that the lowest groove, as in the Indian gun, is 
immediately below the axis of the piece at the bottom of the bore; if 
you follow the course of this groove, you will see it ascend the left side 
of the bore, advance round over the top, and make its exit at the muzzle 
on the right side, after having made, in the Indian gun, two-thirds of a 
revolution. The groove, you observe, has been constantly turning in 
the same direction as the hands of a clock. Now, if we put a studded 
shell into the bore, the grooves will of course force the shell to revolve 
* Vide Eigs. 1 and 2, where the shell is shown in section in the gun, ex centric after being 
rammed home, and centred as it passes along the bore on its exit, the cast-iron of the shell being in 
neither case in contact with the gun-metal of the piece, 
f Vide Fig. 2. 
| Vide Fig. 3; 
