Evening star. [volume] (Washington, D.C.) 1854-1972, 1911-07-23

quadrant and spirit level: the process OF
firing and noting the fall of the shot pro-
Ceeding as before This is done through
every degree M to the maximum eleva-
ton of the weapon. and then reversed
gradually until zero is reached aga in.
From the data so obtained a range table
is worked out for each caliber and class
OF gun.
While the gun is being ranged. the
same firines serve the purpose of check
ing up the allowance for "drift'-thst
Is, the swerving of the shot 70 one side
due to the action of the spinning motion
of the projectile about ITS longest axis.
and measurements are also taken OF the
Jump of the gun az the nluZzie, which
is an upward toss of varying magnitude
due to the yielding of the carriage at
the instant OF recoii.
These latter errors, once determined,
are compensated for by corrections made
when the wea pom is sent hack TO the gun
factory to have It's sighting apparatus
fitted These are individual peculiarites,
differing with each gun, and for that rea-
son each rife must be tested, otherwise
the gun pointer on shipboard will be Sc
riously Handicapped when firing at long
range targets.
The ranging OF the gun incidentally in
wolves thorough testing OF the mount or
gun carriage, because this must be strong
enough to absorb the tremendous recoil
and Set to limit the weapons rearward
movement to q matter of probably not
more than three feet in the case OF our
biggest rifles. One OF our latest J0-caliber
twelve-inch guns and its mount must be
able to absorb through recoil q blow
equal to the colliding force of a 3JO-ton
train brought suddenly to a standstill
when running at the rate of SiXty-seven
miles an hour. for this is the direct coun-
terpart Of the energy centered in the pro-
jectile at the instant of its expulsion from
the gun. Any undesirable yielding or
elasticity In the carriage would affect
both the accuracy of fire and the range
of the shot, and this residence must be
noted to the smallest degree and checked
when passing certain allowed margin.
Our latest big guns have muzzle We
loclty of quite 800 feet a second; and
one of the most interesting branches of
the work at Indian Head is that of meas
uring the speed Of the shell for different
charges of powder. In front of the gun
TO be fired are placed a couple of wooden
frames which are divided into small
blocks by cross-wires. These are called
velocity screens. and each of them is con-
hected electrically with chronographs
which are set in operation successfully
by the action Of the shot itself in flight
AS the projectile passes through the
flrst screen 1t cuts some of the wires and
breaks circuit, and long weight starts
70 drop, the speed Of dropping being n
known factor. When the shot passes
through the second screen-separated
from the first one by an accurately meas
ured dfstance-it, too, cuts wires and
breaks another circuit which causes the
release OF a second and smaller weight
This second weight drives q knife-edge
against the still falling long weight and
hicks the latter: the distance measured
from the bottom of the weight to the knife
~ hn otox hakr
the two measured screens.
In this way 1t is possible to determine
with precision the speed of the proiectile
for the distance given. By varying the
powder charges the shot velocities can
be changed. and this fact Is made use of
in fixing the amount Of powder to be
used in firing against armor plate. where
the attack, although at an actual range
of only 800 feet, Is made to simulate the
force with which the shell would hit at
a much longer distance when using
full measure of powder In ascertaining
the speeds Of recoil and counter-recoil of
a gun, where 1T Is necessary to measure
several consecutive rapid intervals all OF
which may be crowded into wonder
fully brief period Of time. another type
of chronograph IS used by which read
ings Of such refinement can me made
under a magnifying glass that 1t is pos
sible to determine intervals of time II
only one twentyI6ve-thousandth Of a sec
ond. This is not an appreciable period
to the human eye, Yet 1t may be an
important factor in the efficient work
ing of the great guns and may bear
vitality upon their performance In the
hour Of battle.
Probably nothing seems more startling
to the layman than the manner in which
armor-piercing projectiles, bearing blunt
caps upon their points. are able to go
through their own thickness Of hardened
steel when the same shell, uncapped,
would be stopped or shattered by the face
of the plate.
1t does seem strange that a blunted
point can. apparently, accomplish more
than a sharp one. The explanation is