PRINCIPLES OE GUNNERY. 
63 
cartridge is shorter, the energy slightly greater, the pressure in the 
powder-chamber less, and—what is of the most importance—the ratio 
of energy to pressure, p, is the greatest of all the rounds fired. 
When the powder-chamber is enlarged, it must be remembered that 
the strain on the chamber at any point, or the tendency to burst at 
that point, depends not upon the pressure per square inch at that 
point only, but upon the product of the pressure per square inch at 
that point into the number of inches in the diameter; or, in other 
words, if the pressure per square inch in the chamber remains the 
same when the chamber is enlarged, the rending strain on the 
chamber increases as the diameter. 
The disadvantages of windage have already been pointed out, and windage, 
the steps which have been taken to remedy these defects by the 
adoption of gas-checks in the heavy guns. (Page 31.) 
The escape of gas by windage not only causes erosion of the bore, 
but also diminishes the mean pressure on the base of the projectile, 
and consequently reduces its muzzle velocity. With muzzle-loading 1 
guns windage is necessary, to allow of facility of loading ; but in all 
these guns the smallest amount of windage is given consistent with 
ease and rapidity of loading. In service guns there is no difficulty in 
sealing* the windage, by fixing on a gas-check to the base of the 
projectile, so that it may be loaded easily, and that, on firing, the 
shock of discharge may expand it, and seal up the windage. This has 
been successfully accomplished with the heavy guns, resulting in 
increased muzzle velocity, and consequently greater range and accuracy, 
and greater power of penetration. This method of sealing the windage 
will also, in all probability, be applied to muzzle-loading field and siege 
guns of future construction. 
The Committee on Explosives state “that the use of copper gas- 
checks in the 38-ton gun, when firing* 130-lb. charges of l*5-in. cubical 
powder, and 800-lb. projectiles, gives an increase of muzzle velocity of 
about 38 ft. secs, over that obtained with a projectile of the same 
weight with service windage , fired with the same charge—a gain 
equivalent to an increase in the length of the bore of the gun of 
about three calibres. This increase is evidently due to the sealing 
of the windage by the gas-check, whereby the pressure in the powder 
^chamber is increased slightly, while there is also an increased pres¬ 
sure on the base of the shot.'”* 
A comparison of the results obtained with the 35-ton gun of 12-in. Experi- 
calibre and the 38-ton gun of 12*5-in. calibre, illustrates the above prin- 
ciples. The 38-ton gun was 3 ft. longer in the bore than the experi- tongans * 
mental 35-ton gun; but in all other respects they were identical, except 
in calibre. The original charge in the 85-ton gun was 110 lbs. P. 
The increase in muzzle velocity due to the various points of difference 
between the experimental 35-ton gun and the present 38-ton gun, is 
approximately f as follows :— 
* Vide “ Report on the Experimental Rifled M.L. Gun of 38 tons.” 
f The weight of the projectile was 700 lbs. with the 12-in. calibre, and ^Vas increased to 800 lbs. 
with the 12*5-in. calibre. 
