THE ROYAL ARTILLERY INSTITUTION. 
333 
The angles of rifling, and bearings of the different systems, are as 
follows 
Table YII. 
One turn 
in calibres. 
Sine of 
angle. 
Approximate area of 
Name. 
Angle. 
Bearing. 
Bearing 
surface. 
Guiding 
edges. 
Jeffery . 
120 
o 
1 
30 
•0262 
Lead 
sq. in. 
26*2 
sq. in. 
21 
Britten . 
90 
2 
0 
•0349 
Lead 
20*0 
1-0 
Scott .. 
90 
2 
0 
•0349 
Zinc 
19-5 
3-9 
French . 
# 
x 
* 
Zinc 
4-7 
0-6 , 
Lancaster. 
66 
3 
13 
•0561 
Iron 
3-75 
o-o 
Haddan. 
47 
3 
49 
•0666 
Iron 
8*4 
1-0 
Lynall Thomas 
32 
5 
17 
•0921 
Lead 
34-6 
1-9 
Shunt. 
28 
6 
24 
•1115 
Zinc 
7*7 
2-4 
The spiral of the Trench gun is increasing, beginning with 0 at the seat 
of the shot, and ending w T ith 2° 53' at the muzzle. 
With the foregoing we must, however, take into consideration any special 
feature in the form of the projectile, or the mode by which rotation is 
impressed upon it, by which friction is augmented, or the maximum strain 
prolonged. Mr Jeffery’s projectiles differ from Mr Britten’s in having a 
considerable cup at the base, which is expanded by the gas, and must, by 
the pressure of the side against the bore, augment the friction. In Mr 
Lancaster’s system, the major-axis of the ellipse, when the projectile begins 
to rotate, has a tendency to overrun the spiral of the gun, and to pinch, or 
act as a wedge to burst it. The area of bearing surfaces in the above Table 
is the area of so much of the lead as is upset or expanded into the grooves 
in Britten’s and Jeffery’s systems; of the zinc patches, zinc ribs, or other 
projections, in the other systems; and the area of the guiding edges is the 
area of such a length of the sides of the grooves as is at each moment in 
contact with these patches or projections. In the oval bore, where the 
bearings are 3*75 inches long, it is assumed that from compression of the 
ellipse there is actual contact for a width of half an inch at each extremity 
of the major-axis. It appears to show generally that the French shot got 
through the bore with the least resistance of friction, Mr Haddan’s being 
second in order. The Committee, however, prefer the facts furnished by the 
bursting of guns, to any conclusions based on mechanical considerations, 
which involve many uncertainties, and many discordant elements. These 
facts are, 9 cast-iron guns have been rifled on Mr Britten’s system, only one 
has exhibited a want of endurance. A gun of 18-pr. bore (5\29 inches), in 
32-pr. block. No. 9087, burst on 5th April, I860, at the 53rd round. It 
was firing a shot of 34 lbs., with a charge of 6*5 lbs., and Mr Britten has 
shown that, under the circumstances, the strain was more than double that 
of his competitive system. 
(2) The competitive gun, No. 8658, has stood 1286 service rounds.f 
f Since increased to 1486 rounds. 
