The morning call. [volume] (San Francisco [Calif.]) 1878-1895, 1891-11-23

That the forgings possess all the
strength, elasticity and elongation de-
manded of them was found by testing
pieces from each part two inches long by
one-half an inch in diameter. These pieces
having proved satisfactory, the assembling
Of the different parts of the gun was done
last spring and summer, somewhat after
the following manner:
First, the long thick inner tube was bored
out inside and turned down outside, and the
jacket-the first piece to go on-was SINH
larry machned. When these two forgngs
were ready tho tube was placed in the
shrinklng-pi and the jacket in the heating
furnace, where it was expanded sufficiently
to enable 1t to be placed over the rear end
OF the inner tube.
While all the above operations were in
progress measurements of Interior and eX-
terror diameters were constantly being
taken, for on the mathematical accuracy of
these measurements depends the value of
the gun. The strains which the hoops exert
on the parts they bind must be known in
order to insure an absolutely safe gun
hence practice is made 10 conform to theory,
and the parts in size, dimensions and shrink
age are so manipulated as to make them
correspond precisely TO the elements work ed
out on paper by the Bureau OF Ordnance.
NICE WORK IN SHRINKING ON THE JACKET
To proceed with the building OF the gun
The jacket, when sufficiently heated was
swung around by means of overhead cranes
TO the tube and most carefully adjusted in
place The tube and jacket, as one, were
then cooled from the interior Of the bore so
as to make the inner surface of the Jacket
grip the tube before the outer surface was
cooled. The bore of the gun was then
gagged to ascertain how much compression
had been caused by the squeeze OF the
jacket. The remaining hoops were then
shrunk on after having undergone the same
careful treatment as the jacket and after
each layer. the interior Of the gun was again
gagged TO find out the effect of tie compress
sion.
The gun-for now it was built-up gun,
though very rough one-neXt went TO the
lathe. where the bore wac reared out to the
diameter Of the bands. The powder cham
Der was bored out next and the rew-box
cut The gun was then ready for the rihing
The character of the rifiing adopted for
the 12-inch gun, and for all the modern guns
OF our navy, is of the polygrOove system
with au increasing twist. The number of
grooves for all calibers is four times the
caliber of the gun in inches. Hence the
gun now to be put to the proof has forty
eight grooves. The depth of the grooves is
.05 of an inch; their width is .415 of an inch.
The rifiug twist begins at zero and grad
uaily Increases so as TO make complete
turn In distance OF % calibers That is,
at distance of twenty-five feet from the
seat Of tie pro1ectile the shot will have
made one complete revolution about the
axis OF It's lengtn, ana VIII continue so to
revolve throughout its flight
The breech plug fitted to the 12-inch gun
Is In all its principal features the same as
that fitted to all navy guns. 1t is the inter-
rupted screw system. In this the breech
block has thread cut on its outer surface
the circumference of which is divided into
six equal parts. From three of these the
threads are cut away longitudinally. A
similarly divided thread is cut in the rear
end OF the jacket of the gun.
FACTS AND FIGURES.
Following are q few statistics of the gun.
The weight OF the piece alone is 10l. 800
pounds, or, stating these figures in tons, the
Finch gun is 45-tOn gun. The length of
the piece through the axis of the bore is
1868 feet-about the width of the roadway
in the uptown streets Of New York. The
greatest diameter OF the body of the gun is
about 3 feet. The length Of the chamber Is
"a inches and the diameter is 14.5 inches.
which gives chamber capacity Of IL. O43
cubic inches.
The ammunition to be used in the 12-inch
gun for the present Is that known as brown
powder. The charge weighs 425 pounds, II
is TO be put up in several separa te aaftridees
of such weight as to be Conveniently han.
died by the men at thu gun. Each cartridge
IS composed OF scxagonal prisms, each hay
ing hoie snr0ugh the center, so piled one
on tqI OF the other that the small holes In
the prisms will be in line axially. At the
base OF each cartridge is placed a prism Of
quick. burning black powder. The reason
for this is that brown powder is slow burn
ing, and by having black powder prism.
which Is readily iRnited. the gases are dis