The Bamberg herald. [volume] (Bamberg, S.C.) 1891-1972, 1916-03-02
WHY BIG GUNS MISS MARK.
EXPLANATION of Apparent Haphazard
Shell Fire Read About in Reports.

Shell Fire Read About i'll Reports.
Capt. H. J. Jones, inspector OF ord
nance machinery Of the British army
tells the factors affecting the accura-
CIV of fire and range Of big guns, ana
gives some causes that will explain
the apparent haphazard she'll fire that
we read of in the reports from the
war. and why the shots from big
guns so frequently miss their mark,
says the engineer.
/. Whip-The whip or transverse
vibration of the muzzle portion OF
long guns may be the source OF very
large errors. 1t becomes pronounced
with 5O-calibre guns, particularly II
they lack girder stiffness. The droop
of a, 12-inch 50-calibre gun is from
0.3 inch to O.4 inch, and its cantiliver
stiffness such that it makes from l3o
to $50 complete vibrations per Sec
ond. The velocity of the centre OF
the muzzle across the line of depar-
ture arising from this vibration may
be as high as fifty feet per second
with wire-wound guns. Assuming
the mean velocity along the rif1lng
to be 1900 feet per second, we see
that there will be about three COM
pIete vibrations of the muzzle while
the projectile is in the gun. The
projectile may leave the bore with
the centre of the muzzle in any posi-
ton between it's limits of vibrational
displacement, and the error in the
angle of departure is thus quite in
determinate and fortuitous, and the
error of range symmetrically dispos-
ed about the mean
2. Firing Interval-This is the in
terval between the layer pressing the
trigger and the projectile leaving the
bore. With moving gun platforms it
is the main cause of inaccurate shoot
ing. The firing interval is made up
OF two parts, one, from O.08 to O.13
second, during which time the tube
is fired, the charge ignited and the
band engraved, and the other, from
0.O22 to O.035 second, representing
the time of travel of the projectile
along the rifling. In other words, the
firing interval for modern l2-lnch
gun is, on the average, about 0.122
second. These figures, however, may
be greatly exceeded with defective
tubes and firing arrangements.
Modern battleships have a meta
centric height of from 3.5 feet to As
feet, and period of about seconds
for single roll of degrees. This is
equivalent to a maximum angular We
locity of Is minutes of angle per 0.10
second. Hence if we assume that the
layer does not alter the elevation be-
tween the instant of pressing the trig-
ger and the projectile leaving the
bore, the average firing interval
means possible error with the r.
inch Of 1873 minutes elevation. Since
/ minute alteration Of elevation at
10, 900 yards corresponds to about 5
to 20 yards on the water, we see that,
due to q moderate roll of degrees,
every round may be a miss, although
the craftsmanship of the layer be
perfect. Under such conditions firing
Tor individual hits is the merest flu
tility; firing by salvo becomes i'm
perative.
3. Air Spacing-When using re-
duced charges considerable space
exists between the end of the charge
and the base of the shell. Wave
pressures are likely to be set up, CIV
ing rise to irregular burning and ir-
regular muzzle velocity.
4. Propellant-Ths acceptance
limits of a lot of new powder define
the probable variation or muzzle We
locity from round to round. These
limits become extended when lots of
varying ages of different makes are
in use, and, speaking generally, the
mean velocity from any one lot shows
a progressive fall with age.
5. Projectile qualities of
projectiles which effect the ballistic
o-eficient-size, weight, balance,
etc.-will vary from round to round.
The limits of variation are determin-
ed mainly by questions of expense in
manufacture and inspection.
6. Steadiness-The co-eficient of
steadiness is affected by the position
of the centre of form, the speed ro-
tation, initial centering and the &C
tual gun elevation. Projectiles in the
descending branch of high-angle ira
jectories become increasingly un-
stable as the elevation is increased.
Laying-As rule, layers have a
personal prejudice for laying either