South Bend news-times. (South Bend, Ind.) 1913-1938, 1918-11-17
Why Long-Distance Shots Drift Aside
BY Garrett p. Scrviss.

evil YOU please explain the eff
fects OF Fifiing of "A gun on the pro-
lection? If the rifiing is right-hand-
ed. does the projectile drift to the
right, or does il travel in a straight
line?
All elogated projectiles drift i'm
slightly curved path, 10 one side or
the other Of the vertical plane of the
trajectory. the direction of the drift
corresponding with the direction in
which the rifiing turns. Another way
Of putting it is 10 say that the pro-
jeotile drifts aside from the line in
which it is fired, the direction of
the drift being 10 that side toward
which the upper edge, or surface Of
the spinning prOjectile turns as the
latter rOtates on its longitudinal
axis.
For instance, suppose that the
grooves OF the rihng, as they ad-
vance through the bore of the gun
from the breech TO the muzZle, have
a right-hand twist, j. e., turn the
same way as the hands of a watch
then the projectile, which will ac-
quire twist in the same direction
as it passes through the bore, and
will retain that twist on leaving the
muzzle, will, as soon as it comes out
into the air, begin TO sheer off to-
ward the right. But if the rifing of
the gun is left handed, the projec-
tile, after leaving the muzzle, will
sheer or drift toward the left.
The amount of deviation produced
by the drift is, for short ranges. so
slight that il may be neglected, but
in long range firing the drift must
always he allowed for. 1t increases
with the range, and, according TO
some authorities, is approximately
proportional TO the square of the
time of flight of the projectile.
The effect of drift may be coun-
teracted by a special arrangement
of the sights of the gun. Thus, ex-
perience shows that the mean plane
of the trajectory of a projectile af-
fected Dy drift is inclined between
! two and three degrees from the true
vertical
BY tipping the rear sight at the
same angle i'm the opposite direc-
/ ton the plane Of trajectory may
/ be made practically 10 coincide with
! the vertical; or, in other words, the
line of fire will he turned as much
TO one side OF the mark as the drift
of the projectile would carry it to
! the other side.
Recorded mea sures of drift for a
/ l2-inch rifed gun are l 1-2 yards
at a range of 1000 yards, and 1Oa
J yards at q range of $4,000 yards.
The results of drift are oompli-
Gated by windage, which is the
! deviation caused by air currents
/ blowing across the plane OF the
trajectory. and at long distances this
may become very serious. The
amount of drift also varies with the
pitch Of the rifing, the rule being
the greater the twist the greater
the drift The character OF the
surface Of the proiectile affects the
amount OF drift, smooth prejeetiles
being less deviated than studded
ones.
The exact cause Of drift Is con-
fessedly not Vet entirely under
stood. The paths of all rotating
bodies projected rapidly through the
air are subject 10 deviation in one
way cor another. a popular example
is presented by the curves" Of a
baseball, the more or less complete
control OF which has made the fame
I ana fortune of many oelebre TED
| pitchers.
This curving OF a pitched ball is