THE ROYAL ARTILLERY INSTITUTION. 
419 
The half-formecl gun, composed of A and B tubes shrunk up, being next 
placed standing on its muzzle in the shrinking pit, the jacket is heated for 
about ten hours, and shrunk on in the same manner as the B tube; it is 
however (being nearly of the same thickness throughout), allowed to cool 
naturally, and the cold water has to be forced up, fountain fashion, into 
the bore of the gun by a jet round which the muzzle rests. 
The process of building up a 9-inch gun (Mark. IV.) will be very 
similar. There will be, however* three shrinkings instead of only two—viz. 
the coiled breech-piece on the breech end, the B tube on the muzzle end of 
the barrel, and then the outer breech coil over the inner one. 
Processes after the Gun is Built up and before Proof, 
These are :—■ 
(1) Screwing in the cascable. 
(2) Engraving the Koyal cypher. 
(3) Eine boring. 
(4) Second rough cutting of chamber. 
(5) Finished boring. 
(6) Broaching of bore, and finishing of chamber. 
(7) Lapping. 
(8) Bifling. 
(9) Temporary venting. 
(1) The cascable is made of the best scrap iron. It is first forged into a 
simple cylinder; it is then turned, and a bevel thread cut on it. The 
button is turned on it, and a hole (which is afterwards enlarged into the 
loop), is drilled through one end, for the purpose of screwing it into the 
gun. The operation of screwing in the cascable requires great care, for the 
front of it must bear evenly against the end of the steel barrel, and in order 
that this may be the case, the end of the tube is smeared with red lead and 
the cascable screwed in tentatively, then unscrewed again, and filed down 
on the prominent parts, which are indicated by the absence of the red lead. 
This is repeated several times, until the equal distribution of the lead on the 
front shews that it bears evenly against the steel barrel. 
At this stage, one round of thread is turned off the end of the cascable, 
so that there may be an annular space there, which in connection with a 
channel now cut along the cascable and across the thread, will form a gas 
escape, or tell-tale hole, in case the steel barrel should split at tke end. 
The channel is about f th inch broad, and extends -^th inch below the 
thread. In all guns made before the 1st September, 1869, the channel 
comes out directly under the loop ; but in guns made since that date, it 
will be found at the left side of the loop, wdiere it may be more easily noticed. 
The channel ought to be kept clear, and should the barrel be split at the 
end, some gas may be seen issuing from the hole; it is therefore advisable 
to keep an eye on this hole, and to cease firing should it give "warning. 
When at length the cascable fits properly, it is screwed in, and to prevent 
its moving, a hole inches long and £ inch in diameter is drilled and tapped 
through the male and female threads in a slanting direction on the left side, 
and a plug is screwed in, 
