Page:Our big guns.djvu/22

( 16 ) have any reasonable increase of diameter. Moreover, in lieu of a gas-check, and in lieu of studs taking into the rifling, the projectile can be fitted with a driving band made larger than the bore of the gun, which being forced by the powder pressure on the first movement of the shot into the rifle grooves, fills them up, and prevents the passage of gas. Further, the rifle grooves themselves, instead of being few in number and large to receive studs, are made many in number and of but little depth, and thereby the barrel is not so deeply wounded and the projectile is steadied in the bore more accurately; better shooting can be obtained, wads are of course dispensed with, and all chance of double loading is of necessity at an end.

But let us see what demands are made on the gun constructor, by the provision of breech loading, to fulfil these ends.

The breech opening, to be really efficacious, must be of such diameter as to admit of a powder charge having all but the diameter of the powder chamber, that is to say, that in a 12-inch gun the diameter of the breech opening is not less than 16 inches, and in the 110-ton gun is as much as 21 inches.

The pressure although only intended to be some 17 tons on the inch, must, as a measure of precaution, be estimated as considerably in excess of this; but take this 17 tons per inch; in the 12-inch gun, it will give us a total strain of 3400 tons, and in the case of the 110-ton gun a strain of as much as 5800 tons. I will ask those practical men who are here, to remember, how, if for any purpose we desired to fit a vessel, that is to bear some two or three tons per inch water pressure, with a 20-inch cover, we should provide numerous massive bolts and nuts, how we should screw them down one after another, and with what pains we should endeavour to make the joint, and the length of time that would be consumed, even when working at our best, and undisturbed by the attack of an enemy. I will ask that this may be borne in mind, while considering how great must be the difficulties that attend upon making the joint of the breech of even a 12-inch gun, in but a few seconds of time, to resist 3400 tons of pressure, and to be absolutely gas-tight.