Determining Zero Range from Firing Test Results
the opposite question to the one immediately above, and it also
occurs frequently. In this situation, a shooter knows that the center
point of groups fired from his gun at a local target range are located
a certain amount above the point of aim at a measured range distance.
The question then is what is the zero range of the gun?
can answer this question. We will use a specific example to illustrate
how this question is answered. Suppose a shooter has a rifle chambered
for the 25-06 Remington cartridge and uses Federal factory 25-06
Remington ammunition with the 117 grain Spitzer Boat Tail GameKing
bullet. The shooters local target range is 610 ft above sea
level, and he or she shoots on a pleasant day when the local atmospheric
conditions are 30.05 inches of Hg barometric pressure, 75°F,
and 60 percent relative humidity. The center of the groups fired
is 3.25 inches high at 100 yards.
Normal Trajectory Operations list ofInfinity, we first
go to the Load Bullet library and select Federal Cartridges.
From the list of Federal cartridges, we select the 257 caliber and
then select the 25-06 cartridge with the
117 grain Spitzer Boat Tail
GameKing bullet, placing that bullet in the active bullet list on
the monitor. Then, we prepare to calculate a reference trajectory
for this cartridge under the conditions at the shooters local
target range. In the Trajectory Parameters list, the
muzzle velocity is 2990 fps (specified by Federal), the maximum
range is set at 600 yards, the range increment for the print list
is set at 50 yards, the zero range (for this reference trajectory
calculation) is set at 200 yards, the elevation angle is set at
0 degrees (level fire), and the sight height is set to 1.5 inches
for a telescope sight with a 40 mm objective lens. After these numbers
are entered, we accept all the trajectory parameter values listed
in the sidebar on the monitor.
In the Environment Parameters
list, the barometric pressure is set to 30.05 inches of Hg, the
temperature is entered as 75°F, the altitude is entered as 610
feet, and the relative humidity is entered as 60 percent. The wind
velocity is entered as 0 mph, since there is little or no wind on
this day at the target range. All the values of the environment
parameters in the sidebar on the monitor are then accepted, and
a reference trajectory is then calculated.
In the Operations list of Infinity,
we select the Calculate Zero
Operation, and enter the measured range of 100 yards and 3.25 inches
above the line of sight. After accepting these values and pushing
the Calculate button, the monitor shows that the zero
range is 274 yards for this particular situation. Of course, this
is just an example. The same procedure can be repeated for any set
of shooting conditions or firing test results.