42 
PRINCIPLES OP GUNNERY. 
Captain Andrew Noble, of Elswick, has calculated the total pressure 
on the base and also on the studs of a 10-in. shell fired with a charge 
of 70 lbs. of pebble powder, in the case of the gun being rifled (1) with 
uniform twist, or (2) with increasing twist.* 
The uniform twist is taken at one turn in 40 calibres; and the 
increasing twist commences with one turn in 100 calibres, and ter¬ 
minates at the muzzle with one turn in 40 calibres—the same as the 
uniform twist at the muzzle; so that the shell, while moving with the 
same velocity at the muzzle, would have the same muzzle velocity of 
rotation in both cases. 
Travel of 
shell. 
Total pressure 
j Corresponding 
velocity in both 
cases. 
Total pressure on studs. 
on base of shell 
in both cases. 
Uniform twist. 
(1) 
Increasing twist. 
(2) 
ft. 
tons. 
f.s. 
tons. 
tons. 
•000 
0 
0 
0-0 
o-o 
•333 
1547 
411 
68-5 
31-2 
•945 
1077 
675 
47-7 
28-7 
1-834 
781 
873 
34-6 
29-0 
2-723 
621 
992 
27-5 
30-2 
3-612 
510 
1078 
22-6 
31-4 
4-500 
424 
1146 
18-7 
32-3 
5-389 
356 
1200 
15-8 
330 
6-278 
305 
1245 
13-5 
33-8 
7-167 
268 
1282 
11-8 
34-5 
8-055 
240 
1311 
10-6 
35-2 
8 '944 
220 
1333 
9-7 
35-8 
9-833 1 
205 
1349 
9-1 
36-3 
It appears from this table that the pressure on the studs at the com¬ 
mencement of motion is much less in the increasing than in the 
uniform twist, and consequently that the studs on the projectile would 
not be so severely strained, nor the driving sides of the grooves of 
the gun so much indented in the increasing as in the uniform twist. 
This is what is found to be the case in practice, and is the reason why 
the increasing twist has been preferred to the uniform twist for the 
heavier natures of guns. 
Velocity The velocity of recoil is generally taken as the velocity imparted to 
the gun and carriage by the discharge of the piece. It is the greatest 
when the projectile leaves the muzzle. 
Let V" be the maximum velocity of recoil, 
v the muzzle velocity of projectile, 
w the weight of projectile, 
w' the weight of charge of powder, 
W" the weight of gun and carriage. 
Then, if the momentum of the gun and carriage be taken equal to 
the momentum of the projectile, 
TF" V" == {to -f- Cm') v, 
nr V " — + Cw') v m 
' W ’ 
* See “ Proceedings, R.A. Institution,” Yol. VIIL p. 365» 
