420 
MINUTES OF PROCEEDINGS OF 
(2) While the cascable is being prepared. Her Majesty’s monogram is 
engraved in front of the vent, the outline being marked on the gun by 
means of a perforated brass plate, rubbed over with charcoal. 
( 3 ) The gun is next removed to the boring mill, where it is fine bored 
to 8"-9. 
( 4 ) The chamber is next roughly bored out with the same boring head 
as before. 
( 5 ) The finished boring to 8"*997 is then performed. 
The fine boring and the finished boring are effected with the boring head 
used in the the second rough boring, and together occupy twenty-six hours. 
(6) In each boring the cutters wear a little during the operation, so 
that the bore becomes slightly taper towards the breech. This is of no 
consequence in an outer tube, as the exterior of the inner one can be turned 
accordingly, but the bore of the gun must be cylindrical, so broaching is 
employed—that is, boring the barrel by means of a cylindro-conoidal head, 
fitted with four long cutters at right angles to one another, and slightly 
tapering. The cutters are edged on the front as well as on the side, as the 
chamber is also finished off at this time, and for this latter purpose there is 
also a peculiar centre cutter for the very end of the bore. 
(7) Still, however, the bore is not yet truly cylindrical, and “ lapping ” is 
resorted to. In this no cutter is used, but a wooden head, covered with 
lead and smeared over with emery powder and oil, is worked up and down 
at those portions of the bore which are indicated by the gauges as im¬ 
perfect. 
(8) The 7-inch M.L. guns are rifled with a uniform spiral— i.e. with 
grooves having the same amount of twist at every point of the bore; and all 
the higher natures with a uniformly increasing spiral— i.e . uniformly increasing 
from the breech to the muzzle. The advantage of an increasing spiral is, 
that the inclination of the grooves, being little or nothing at the breech, 
the projectile’s initial motion is not checked by any resistance offered to the 
studs. The projectile therefore moves quickly from its seat, and relieves 
the breech a good deal from the strain of the discharge. 
The machine is a horizontal one. The gun is fixed stationary in front of 
it, in a line with the rifling bar. The bar goes through a double motion of 
progression and partial rotation. Did it simply progress along the bore, a 
straight groove would be cut, but as we want a spiral groove, the partial 
rotation is necessary. 
The progressive, or rather the backward and forward motion, is given by 
a fixed screw which stretches along the middle of the bed (as in the boring 
machine), and passes through a nut in the saddle to which the off end of the 
rifling bar is attached. 
The proper amount of rotation is obtained by means of a rack which 
works into a pinion on the end of the bar, according as the bar progresses 
and slides across the saddle, as it is constrained to move along a tangent or 
copying bar which is inclined to the side of the machine at the required 
angle of the rifling. The greater therefore this angle, the quicker does the 
rack slide and the bar revolve, and the sharper is the twist of the groove 
cut in the gun. 
