Topic of the Month:
February 2002
Point Blank Range
A common belief, with roots back to old western movies
and Cop shows, is that point blank range is an unspecified distance, very close to the
muzzle of the gun, in which the shooter just can’t miss the target no matter where he
aims. A more modern and useful definition is that point blank range of any gun is the
maximum distance out to which the shooter can hold right on a game animal and be assured
of a hit within a vital zone of the animal. It is a measure of how flat a gun will shoot.
For varmints the vital zone may be 2 to 4 inches (+/- 2 inches) while for deer sized game
the vital zone may measure 10 inches (+/- 5 inches) or more. Fig. 1 shows the vital area
of deer sized game.
Fig. 1- Vital zone of deer size animal
For example, let’s look at the trajectory for the .223
Remington, shooting a 55-gr. bullet with a muzzle velocity of 3,600 f.p.s. The bullet
coefficient is 0.237. The scope-mounted rifle is zeroed for 200 yds. The end range is set
at 400 yd. and the trajectory range increment is 20 yds. If we were trying to dispatch a
varmint that had a kill zone of 4 inches and we were using the .223 Remington as sighted
in Fig. 2, the bullet would be within the 4 inch span (+/- 2 inches) from the muzzle to
about 250 yds.
Fig 2-Trajectory for .223 Rem., zero at 200
yds.
However, we can improve on the maximum point blank range by
setting our sight-in zero to a longer range. If we increase the sight-in zero to 250 yards
you can see from Fig. 3 that the bullet will stay within the +/- 2-inch range from the
muzzle to about 290 yards down range.
Fig. 3- Trajectory for .223 Rem., zero at
250 yds
We were able to determine the maximum point blank range for
the example by increasing the sight-in zero range, by trial and error, until the point
blank range no longer fit the 4-inch span we allowed the bullet to deviate from the line
of sight. Fortunately, with many of the ballistic programs now available there is no need
to go through a trial and error procedure to determine maximum point blank range when this
can be done by the computer in a few seconds. The Load From a Disk program advertised on
this web site not only solves for the maximum point blank range, but also gives you the
bullet impact at a standard range of 100 yards. Note from the example that the zero range
for the maximum point blank range was 250 yards. Since most target ranges don’t have
a target holder at 250 yards you can sight in your rifle to shoot 1.85 inches high at 100
yards to give you a 250 yard zero. The computer results are given as hard numbers so no
trajectory interpretation is required. The only input values required are muzzle velocity,
bullet BC and the vital zone dimensions (+/- 2.5-inches to +/- 5.0-inches).
Watch our web site for the next topic of interest
"Shooting Sabots." Until then, shoot safely and know where your bullets are
going.
Sincerely,
The Ballistician
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