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To insure the true direction of the shot, the gun must be rifled, and means must be provided, as far as practicable, to neutralise the rush of powder gas and mitigate its erosive effects.
The principal forging for a gun is now of an enormous weight. The ingot, as I have told you, has to be some 66 per cent, heavier than the forging, involving change in composition by the separating out of the carbon while cooling, and involving also the chance of concealed flaws, which no subsequent manipulation can cure. The resulting forging can only be tested for quality in places, and no known, certain, test exists, for concealed flaws. The very act of forging, especially under the hammer, and the act of oil-hardening, are each likely to set up internal strains, the effects of which may be going on for months, and may end in spontaneous rending asunder, as happened with certain cast-iron guns to which I have alluded, and as has happened in more than one instance in the case of steel guns, or of the forgings for steel guns.
The truth is, until some one is found, who can see into the very inside of the metal of the gun, and can do so in every part, and until such a person, even if he could see, possessed the ability by mere inspection to judge of quality, and of condition, no gun can be pronounced absolutely and undoubtedly trustworthy. You may by experience based on experiment, by vigilance in selection of material, by such tests of that material as you can make during manufacture, and by proof of the gun when made, so far diminish the chances of failure, that you are quite prepared to stand beside the gun when fired, as you are quite prepared to take your voyage in an ocean steamer, or to stand alongside a steam boiler; but as in neither the instance of the ocean steamer, nor in that of the steam boiler, can you say with absolute certainty you are safe, so in the instance of the gun, you must be prepared to admit that each time you fire it you run some risk, and you must for the present, be content to find that other nations are in precisely the same condition.
