GUNS Magazine January 1956

Many have the mistaken notion that
a bullet travels in a straight line for a
certain distance after leaving the muzzle,
this distance varying with the power
of the gun. This, they think, is what
is spoken of as point-blank range. Others
will even have you believe that a
bullet rises for a distance after leaving
the muzzle.
The probable reason for these two
misconceptions is the failure to distinguish
the difference between the line of
bore and the line of sight. If they would
just stop and consider how utterly impossible
it is to lick gravity, they would
understand that a bullet must start to
fall the instant it leaves the barrel,
where gravitation takes over.
Line of sight is a direct line from
the eye, through both the rear and
front sight, to the target.
Line of bore is a direct line from
the cartridge in the, chamber, through
- the bore to infinity.
These two lines are never exactly
2
~arallel to each other.
Here is what happens when we sight
in a gun for a given distance. We raise
the rear sight until by test shooting we
have the bullets striking in the center
of the target. Our line of sight is still
a direct line from the eye, through both
the rear and front sight, to the target.
But if we look through the bore we
find that the line of bore is aimed above
the target.
This is to take care of bullet drop
caused by gravity. The amount of this
drop, and the discrepancy between the
line of sight and the line of bore, varies
with the distance from gun to target,
bullet velocity, its shape and weight.
The bullet does rise above the line
of sight. It has to (except at absurdly
short distances), but it does not and
can not rise above the line of bore. The
line of bore controls the line of de-
parture of the bullet from gun muzzle
to target, and we control the line of
bore with the line of sight.
The line of bore starts the bullet on
its way toward the target with just the
right amount of angle above the line of
sight to compensate for the bullet's
drop, caused by gravity.
For use in ballistic tables it is com-
mon practice to take the height of tra-
jectory (height above line of sight) at
half way from gun muzzle to target,
and this is called mid-range trajectory.
WIND DEFLECTION IN INCHES
50 yds.
.22 Long-Rifle
Standard -
Velocity
100 yds.
.22 Long-Rifle
50 yds.
Miles
per
hour
369
o'clock
winds
Spark photo of .22 bullet at speed
slower than sound shows heavy air
compression waves which build up at
bullet nose and eddy currents behind.
- -
Supersonic bullet has crashed through
-pressure barrier and is less disturbed
in flight by front air resistance but tur-
bulence and shock still affect rear.
The extreme height of trajectory, how-
ever, is not at this point, but at approx-
imately three-fifths to two-thirds the
distance from gun to target, again de-
pending on bullet weight, shape, veloc-
ity and, of course, range.
The longer a bullet is in the air the
slower it travels, due to air pressure;
and the slower it travels the faster is
its rate of fall in relation to its feet-
per-second of forward movement. Con-
sequently the angle of fall below the
line of bore is very slight near the muz-
zle, but increases as the range increases.
As an example of bullet movement,
the maximum ordinate (extreme height
of trajectory) when firing at 1000
yards with the military .30-'06 car-
tridge, using the M-1 load which was
used by our government from 1925 to
1940 (and which was the best car-
tridge, incidentally, of any this coun-
try has ever used) was 10.5 feet above
the line of sight. Firing the same car-
tridge at 200 yards, the maximum ordi-
nate is but 0.28 feet. The 1000 yard
figure for the same cartridge, when
using the load we had in World War
I, was 15.2 feet. I do not have the
figures for the present M-2 load, which
. .