FM 23-91.pdf - Marine Corps

FM 23-91
variations in the weapon, weather, and ammunition at a given time and place. The
atmospheric standards in United States firing tables reflect the mean annual conditions in
the north temperate zone. The main elements measured in experimental firing are angle of
elevation, angle of departure, muzzle velocity, attained range, drift, and concurrent
atmospheric conditions.
Figure 2-4. Example of Firing Table 4.2-K-2.
2-11. PURPOSE
The main purpose of a firing table is to provide the data required to bring effective fire on
a target under any condition. Data for firing tables are obtained by firing the weapon at
various elevations and charges.
2-12. UNIT CORRECTIONS
Firing tables describe unit corrections as range corrections for an increase or decrease in
range, wind, air temperature, density, and projectile weight, followed by the unit value in
meters.
a. Each correction is computed on the assumption that all other conditions are
standard. However, any correction will differ slightly from that computed if one or more
of the other conditions are nonstandard. The amount of difference depends on the effect
of the other nonstandard conditions. The effect of one nonstandard condition on the
effect of another nonstandard condition is known as an interaction effect. The effect of a
nonstandard condition depends on how long the projectile is exposed to that condition.
b. The extent to which weather affects a projectile can be determined from a
meteorological (MET) message if the maximum ordinate achieved is known. Corrections
for those effects can be compensated for in the appropriate firing tables.
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