t greatly reducing
the velocity of the shot has become imperative. It would be impossible
even to recapitulate the conflicting arguments of the experts on this
subject, within the limits of this paper. It does appear from recent
experiments, however, that this result can be accomplished by
compressing the powder, so that, we will suppose, it burns slowly and
overcomes the inertia of the shot before the whole mass is ignited; and
also by leaving an airspace around the cartridge, into which the gases
probably expand while the inertia of the shot is being overcome, thus
avoiding the excessive blow upon the walls of the gun during the first
instant of the explosion. Whatever the cause may be, the result is of
the highest importance, not only as to cast-iron guns, but as to all
ordnance, and warrants the most earnest and thorough investigation. The
principles of the Armstrong gun differ in some degree from all those
mentioned, and will be better referred to under the head of _Heavy
Ordnance Described_. The Armstrong gun is thus fabricated. A long bar of
iron, say 3 by 4 inches in section, is wound into a close coil about 2
feet long and of the required diameter,--say 18 inches. This is set upon
end at a welding heat under a steam-hammer and "upset" into a tube which
is then recessed in a lathe on the ends so as to fit into other tubes.
Two tubes set end to end are heated to welding, squeezed together by
a heavy screw passing through them, and then hammered lightly on the
outside without a mandrel. Other short tubes are similarly added. Five
tubes of different lengths and diameters are turned and bored and shrunk
over one another, without successively increasing tension, however, to
form a gun. The breech-end of the second tube from the bore is forged
solid so that its grain will run parallel with the bore and give the
gun longitudinal strength. Both the wedge and the screw breech-loading
apparatus are employed on guns of 7 inches bore (110-pounders) and
under. It will thus be seen that the defects of large solid forgings are
avoided; that the iron may be well worked before it is formed into a
gun; and that its greatest strength is in the direction of the greatest
strain; and on the other hand, that the gun is weak longitudinally and
excessively costly, (the 7-inch gun costs $4,000, and tin 10-1/2-inch,
$9,000,) and that the material, although strong and pretty trustworthy
in the shape of bars, has insufficient elasticity and h