THE 80-TON GUN. 
849 
inclusive of the gas-check. This important adjunct consists of a stout 
copper ring ; flanged round the rim, and is applied at the base of the 
projectile; so that the pressure of the gas drives the flanged rim out 
against the surface of the bore; sealing the windage completely. These 
gas-checks were secured to the shot by a strong screw in the middle— 
a method of fastening which will probably be superseded by a more 
convenient automatic attachment. 
In the centre of the screw fastening on the gas-check is placed a 
crusher-gauge; to register the maximum pressure of the gas on the 
base of the shot. There is fortunately no occasion for me to describe 
the scientific instruments used to determine pressures and velocities; 
since a paper on these subjects is being prepared for the present issue 
by one specially qualified for the task (Capt. C. Jones, R.A.); and 
therefore I merely refer those unacquainted with the details of the 
apparatus to his explanations. As previously mentioned; on firing a 
built-up gun for the first time; a slight re-adjustment of the parts 
sometimes takes place; and hence it is always desirable to fire a few 
rounds before piercing the sides for the insertion of crusher-gauges. 
It is found by experience that the highest pressure in a gun is usually 
encountered at the centre of the bottom of the bore; and it therefore 
is advantageous to possess the means of ascertaining the amount of 
this pressure; even with guns not pierced for gauges. This object has 
been attained by the use of a copper cup; which fits the end of the 
bore; and which carries; screwed into its base, a crusher-gauge; pro¬ 
jecting into the end of the cartridge. This gauge gives fairly accurate 
results, though it is not so trustworthy as those of the usual form. It 
is liable to be jarred and shaken by the discharge, and thus errors are 
occasioned—which, however, lie almost invariably in the direction of 
excess, and therefore on the side of safety. 
The 80-ton gun, when ready for firing in its 14J-in. calibre, was 
mounted on its carriage by the hydraulic crane in the Royal Gun 
Factories, and was drawn to the Butt by two locomotives—one being 
that in use in the Department, and the other a slightly more powerful 
one, borrowed from the South-Eastern Railway Company; and no 
great difficulty was experienced in getting it to the firing position on 
the rails at the foot of the recoil slope. The first experiment consisted 
in firing—to prove the gun—six rounds of increasing* charges of the 
powder which had proved suitable to the 38-ton guns, and had been 
adopted for them. Although no holes, except that for the vent, were 
yet pierced in the sides of the piece, still, by means of the gauges in 
the cup at the bottom of the bore and in the base of the shot, sufficient 
information was obtained to warrant the gradual enlargement of the 
charges from 170 lbs. to 240 lbs., and the surprising velocity of 1550 f.s. 
was realised without exposing the gun to any very inordinate strain. 
On the successful termination of the proof rounds, the gun was taken 
back to the factory, examined, and found entirely uninjured. It was 
then pierced with holes in its axis and sides to take seven crusher- 
gauges, and sent back to the Butt. 
Table C. (compiled by Capt. Jones) gives full details of all the 
rounds fired up to the present time from the gun, and I will make a 
few remarks on the form into which Capt. Jones has thrown the 
