470 
THE 80-TON GUN. 
length of the cartridge was 36*5 ins. Comparing this with round 16, 
Table C, we observe that the length of a 250-lb. charge, air-spaced to 
30 cub. ins., is 44*2 ins.—the difference being rather more than half a 
calibre. This lengthening of the cartridge is of course equivalent to 
shortening the gun by that amount, as far as the travel of the shot is 
concerned. A very sensible loss of velocity is thus occasioned, and it 
would evidently be desirable to afford more room for the charge inside 
the bore. To accomplish this it is necessary to enlarge the chamber,* 
so that the cartridge can be shortened, and the enormous and incon¬ 
venient length required for heavy charges lessened. A reference to 
Table C will show that with 300-lb. charges in a 15-in. calibre this 
length reaches nearly 53 ins. Accordingly it was determined to take 
the 80-ton gun back to the boring machine and to enlarge its chamber. 
The gun was originally constructed with a view to its being bored out 
to a 16-in. calibre, and hence there could be no difficulty or risk in 
carrying the chamber to that size, while leaving the portion of the bore 
in front of the cartridge at a diameter of 15 ins. Of course this 
enlargement was not so great as could be desired; but it was thought 
that if the principle was correct, sufficient indication of its beneficial 
action would be obtained. 
The enlarged portion of the bore was 40 ins. long, and was capable 
of holding 263 lb. at the rate of 30 cub. ins. to the pound, or 320 lb. 
fulled rammed up. It subsequently proved that it would have been 
better to have made the chamber a few inches longer; but this was 
not foreseen, and too much time would have been lost in removing the 
gun back to the factory and continuing the enlargement for a greater 
length, so as to suit the larger charges fired toward the end of the 
experiment. * 
It was determined to begin with charges of 260 lb. with each of the 
cubical powders allotted to the trials, and to increase this amount suc¬ 
cessively by 10 lb. at a time. Each cartridge was to be pressed to 
the mouth of the chamber— i.e., to 40 ins.—and thus as the charge was 
increased the air space was diminished; so that, had the pressures 
permitted it, the chamber would have been eventually filled with a 
rammed-up cartridge. 
Table D gives the particulars of the rounds fired under these con¬ 
ditions. The comparative rounds fired in the same calibre but in 
the unchambered state are added in italics beneath those of similar 
character, and the order adopted is that naturally given by the several 
powders tried. 
The proposed arrangement of preserving equal lengths for the car¬ 
tridges was adhered to for nine rounds, after which it was decided to 
return to the 30 cub. in. air space. Examining rounds 33, 34, and 35, 
each fired with 260 lb. of the brands before used, and comparing them 
with rounds 23,17, and 18 respectively, it appears that in each case the 
* A sketch of the origin and progress of the principle of applying an enlarged chamber to 
muzzle-loading ordnance in order to gain increased power, will shortly he given in a paper by the 
present writer on the new experimental field guns, which are constructed on this method, as pro¬ 
posed in 1873 by Br.-Gen. Campbell (then Superintendent of the Boyal Gun Factories). 
