THE ROYAL ARTILLERY INSTITUTION. 
209 
Object of increasing spiral . 
The object of rifling a gun with an increasing spiral is to decrease the 
strain on the powder chamber of the gun, as the projectile has only to move 
directly forward at the moment of starting, instead of being forced simul¬ 
taneously into rotation. This of course also has an effect on the vent, it 
being found that, of two 7-in. guns, fired under the same conditions for a 
number of rounds by the 0. S, Committee, the vent of the one. with the 
uniform twist was more enlarged than that of the one with the gaining twist. 
The difference was small but decided. 
Difference of initial velocity , 
Owing, however, to the shot leaving its seat in the gun with the gaining 
twist more readily than in the other, less of the powder charge is consumed 
before it moves, and the initial velocity will be slightly less, being in a 
proportion of 1444 to 1465 feet per second. 
This difference in velocity, however, is recovered during flight, owing to 
the front studs being smaller, and offering therefore less resistance to the 
air. The difference of initial velocity will represent the amount of relief to 
the powder chamber. 
These experiments shewed no difference of any practical importance 
between the two guns, as to range or accuracy. 
Projectiles for the 7" and 9" guns. 
The projectiles for these two guns are fitted with rows of gun-metal studs, 
screwed in, rounded to fit the grooves, two in a row; the number of rows 
corresponding to the number of grooves in the gun. 
Tor the 7-in. gun with uniform twist, the two studs are of the same size, 
but for the 9-in. gun with increasing twist, it is evident that if they were of 
the same size, the front part of the shot would have a tendency to rotate 
more rapidly than the back part, so that, even if 
the gun could be loaded, on leaving, either the 
front studs would be torn off, or the shot w T ould 
jam. 
The Trench have only one stud in this case, so 
that the shot leaves the gun with only one bearing, 
which would be likely to affect the accuracy of the 
shooting. 
Major Palliser, to remedy this, proposed to 
make the front stud smaller than the back one, 
the latter fitting the groove. Tig. 2 (not to scale) 
represents a section through the bore of a gun 
with an increasing twist, with a projectile in the 
position the studs would occupy at the breech and 
muzzle, without taking friction into account. 
The line A A, touching the driving sides of the 
studs (or the sides which bear against the grooves 
on leaving the gun), makes with the axis of the 
Eig. 2, 
