416 
MINUTES OF PROCEEDINGS OF 
The two coils, being made and wielded in the usual way, they are faced 
and reciprocally recessed to the depth of about one inch, and then united 
together endways by expanding the faucit of one coil by heat, and allowing 
it to shrink round the spigot of the other. This sticks the two coils suffi¬ 
ciently tight together to admit of the tube thus formed being placed 
upright in a furnace, whence, when it arrives at a white or welding heat, it is 
removed to a steam hammer, and receives on its end six or seven pressing 
blows which weld the joint completely. The weight of the tube in this 
rough state is about 55£ cwt., but when finished as it is on the gun it only 
weighs 31 cwt. 
The B tube is next rough turned, in which process a rim is formed near 
the muzzle for the convenience of lifting the tube in “ shrinking.” After 
this, the tube is rough and fine bored in the same horizontal machine. The 
tube is fixed truly central in a saddle capable of sliding along the frame of 
the machine. The boring bar, having two cutters placed adjoining and 
opposite, is passed through the tube and fixed at each end of the machine. 
The bar revolves while the saddle moves forward, and thus the boring is 
effected. The difference between the rough and fine cutters is (as generally 
the case) that the former are deep and narrow, and the latter shallow and 
broad. 
The interior of the B tube having thus been brought to the degree of 
smoothness requisite for close contact with the steel barrel, is gauged every 
twelve inches down the bore, and also at the shoulder. To the measurements 
thus obtained, the calculated amount of shrinkage (0" # 003 at the muzzle, and 
increasing up to 0"*03 at the other end), is added; a plan is made out 
according to which the exterior of the A tube (or rather that portion of it 
on which the B tube is to go) must be turned down, in order that it shall 
be exactly larger than the bore of the tube by the required amount of 
shrinkage at the respective parts. 
The plan (as illustrated by the annexed drawing), is made on a slip of 
paper, and together with a corresponding series of accurately measured 
horseshoe gauges, is furnished to the turner, who turns down the muzzle 
end of the A tube accordingly. 
The reason an inner tube is turned to suit an exterior one, instead of 
the latter being bored to suit the former is, that it is much easier to turn 
than to bore to very exact dimensions, on account of the great command 
which the operator has over the turning lathe, and the facility he has of 
testing his work by gauges, and correcting it by emery powder and oil. 
The Breech Coil or Jacket . 
The breech coil or jacket is composed of a triple coil, a C double coil, 
and a trunnion ring, made and welded together as follows:— 
