Source: https://www.globalsecurity.org/military/library/policy/army/fm/6-40/Ch7.htm
Timestamp: 2018-11-14 04:55:33
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FM 6-40 Chptr 7 Firing Tables ï»¿
This chapter implements a portion of QSTAG 224.
Field artillery firing data are determined by use of various firing tables and equipment. These tables contain the fire control information (FCI) under standard conditions and data correcting for nonstanadard conditions. These tables and equipment include the tabular firing tables, graphical firing tables, and graphical site tables. The tabular firing tables are the basic source of firing data. They present fire control information in a tabular format. The data listed are based on standard conditions. The GFTs and GSTs are graphical representations of the tabular firing tables.
This section implements STANAGs 4119 and 4425 and QSTAG 220.
Tabular firing tables are based on test firings and computer simulations of a weapon and its ammunition correlated to a set of conditions that are defined and accepted as standard (See Figure 7-1.) These standard conditions are points of departure. Corrections are used to compensate for variables in the weather-weapon-ammunition combination that are known to exist at a given instant and location. The atmospheric standard accepted in US firing tables reflect the mean annual condition in the North Temperate Zone. TFTs are developed for weapons ranging from crew-served to heavy artillery. The format of artillery firing tables are based on standardized agreements, and with small exceptions, are very similar.
7-1. Elements and Purpose
a. The principal elements measured in experimental firings include the following:
Angle of departure.
Achieved range.
Concurrent atmospheric conditions.
b. The main purpose of the TFT is to provide the data to bring effective fire on a target under any set of conditions. Data for firing tables are obtained from firings of a weapon conducted at various quadrant elevations. Computed trajectories are based on the equations of motion and are compared with the data obtained in the firings. The computed trajectories are adjusted to the measured results and data are tabulated. Data for elevations not fired are determined by interpolation. Firing table data define the performance of a projectile of known properties under standard conditions.
7-2. Cover Information
The cover of the TFT provides information concerning the weapon system(s) and projectiles to which data in the TFT apply. Projectiles listed on the cover are in the same projectile family because of ballistic similarity.
NOTE: The 155-AM-2 TFT is used as the example throughout this section. Figure 7-2 identifies acronyms and abbreviations for the TFT shown in this section.
a. Introduction. The introduction contains general information about the weapon, ammunition, and the TFT. This information specifically includes the items below.
(2) Table of symbols and abbreviations (used in the TFT).
(3) General information.
(4) Interchangeability of ammunition. This table shows the ammunition combination held in stock by other NATO nations for a particular weapon caliber that can be used by the US during combined operations, to include training exercises. Because of safety, the ammunition listed in the shaded portions may only be used in combat operations. (See Figure 7-3.)
(5) Weapon characteristics. (See Figure 7-4.)
(6) Projectile-fuze combinations and mean weights. (See Figure 7-5.)
(7) Equivalent full service rounds. These tables provide information on tube wear and erosion. These data are used to determine the number of equivalent full service rounds fired and the expected muzzle velocity loss due to wear. The values listed in these tables are based on firings of the highest charge used by that weapon system. (See Figure 7-6.)
(8) Approximate losses in muzzle velocity. The tables maybe used as a guide in estimating muzzle velocity variations from the firing table standard that are due to uniform wear in the M185 and the M199 cannon tubes. (See Figure 7-7.)
NOTE: The M199 cannon tube needs to be corrected for certain increases in muzzle velocity, see FT 155-AM-2, page V.
(9) Explanation of tables.
(10) Example of met message and sample problems.
(11) Explanation of the probability table.
(12) Table of natural trigonometric functions.
(13) Charge selection table. This table provides guidance to the FDO on the selection of the charge to fire based on range and probable error. Enter the table with the range to target expressed to the nearest listed value, and choose the charge to fire. The gray shaded area shows those charges with the lowest probable error in range and thereby the charge that should be selected given no other considerations. (See Figure 7-8.)
(14) Table of conversion factors. (See Figure 7-9.)
b. Part 1. Part 1 of the TFT contains firing data and corrections for the base projectile. It is divided into Tables A through J. Additional Tables K through M may be provided in some TFTs, but the format and content vary.
7-3. Table A
a. Table A is used for the solution of a concurrent met. It is used to select the line number of the met message. The entry argument for this table is quadrant elevation. The QE best describes the maximum ordinate of the trajectory and, thus, the portion of the atmosphere through which the projectile will pass. The height of the trajectory is determined by computer simulation using equations of motion. Table A also assumes that the target is at the level point of the trajectory. If there is a large vertical interval (either positive or negative), the met message line number selected will not exactly describe the atmosphere through which the projectile passes. This will cause only a small error in manual computations.
b. Enter Table A by using the left column with the adjusted quadrant elevation to a target. Extract the line number of the met message from the right column. (See Figure 7-10.)
7-4. Table B.
a. Table B is used in the solution of concurrent and subsequent met. This table is used to determine the value of complementary range (change in range) to correct for the effects of complementary angle of site. Complementary ranges were determined by computer simulations of the trajectory at each listed range and vertical interval. Table B has two entry arguments; they are chart range to a target expressed to the nearest 100 meters and the height of target above gun (vertical interval) expressed to the nearest 100 meters. Table B is entered from the range column along the left side, with the chart range to a target; and along the top of the table with the height of target above gun (vertical interval). Extract the value of complementary range where the two columns intersect. The complementary range is the number of meters of range correction that corresponds to the complementary angle of site. This range correction is measured at the base of the trajectory. The sum of the complementary range and the chart range, expressed to the nearest 10 meters, equals the entry range. This is the most accurate range for entry into Table F to extract firing data and range corrections.
b. Table B is also used to determine the line number from a ballistic met message for use in subsequent met applications. The table is divided by heavy black lines. These lines form the boundaries of the met zone. The line number may be determined by following the lines between which the complementary range is extracted to the outer edge of the table. The bold number in the margin is the met line number. The met message line numbers were determined by the same method used in Table A. (See Figure 7-11.)
NOTE: Table A is more accurate in the determination of the met message line number to be used in the solution of concurrent met.
7-5. Table C
Table C is used in the solution of concurrent and subsequent met. It is entered with the chart direction of wind. The chart direction of wind is the angle formed by the intersection of the direction of the wind from the met message and the direction of fire (that is, the horizontal clockwise angle from the direction of fire to the direction of the wind). This table divides a 1-knot wind into crosswind and range wind components. Components for crosswind and range wind are then extracted. The extracted values are described as the components of a 1-knot wind. The range wind component is the percentage of the wind speed that acted as a range factor. The crosswind component is the percentage of the wind force that acts to blow the projectile laterally and is translated into a lateral correction factor. (See Figure 7-12.)
NOTE: Table C is based on chart direction of wind only and, thus, is the same for all charges and all weapons.
7-6. Table D
a. Table D is used in the solution of concurrent and subsequent met. The values extracted from the table are standard departure of air temperature and density as a function of height. They have been converted to a percentage of standard. This table provides a correction based on a standard departure to correct the temperature and density in the met message (which is measured at the altitude beginning at the meteorological datum plane [MDP]) to values as if they would be measured initially from the unit altitude.
b. Table D is entered with the height of the unit above or below the MDP or met station. The difference in height is entered on the left side in hundreds of meters and along the top of the table in tens of meters. Extract the corrections to density and temperature from the intersection of the two columns. (See Figure 7-13.)
7-7. Table E
a. Table E is used in the solution of concurrent and subsequent met. The extracted values list the effect on muzzle velocity (in meters per second) of nonstandard propellant temperatures.
b. Table E is entered with the temperature of the propellant in degrees Fahrenheit by using the left column or Celsius by using the right column. An effect in meters per second is extracted from the center column. This is the change in muzzle velocity because of the temperature of the propellant. Interpolation is needed to determine precise values from this table. (See Figure 7-14.)
7-8. Table F
a. Table F lists information needed to determine firing data to attack a target and for solving concurrent and subsequent met. Table F is comprised of 19 columns. Columns 2 through 7 provide information for the computation of basic firing data and are based on a set of standard conditions. The remaining columns provide corrections to range and deflection for nonstandard conditions. The asterisks extending across the table denote the changeover point from low-angle to high-angle fire. (See Figure 7-15.)
(1) Range (Column 1). This is the distance measured from the muzzle to the target on the surface of a sphere concentric with the earth. When range is used as the entry argument for this table, it is expressed to the nearest 10 meters. Interpolation is necessary.
(2) Elevation (Column 2). This is the angle that the cannon tube is elevated from the horizontal plane (base of trajectory) to cause the round to impact at the level point for a given range. The elevations listed are the elevations required under standard conditions to achieve the ranges listed in column 1.
(3) Fuze setting for a graze burst (M564) (Column 3). This is the number of fuze setting increments necessary to cause the fuze to function at the level point at the given range under standard conditions. The values listed are for fuzes M564 and M565. The values are expressed in fuze setting increments.
(4) Change in fuze setting ( FS) per 10-meter decrease in height of burst (Column 4). This is the adjustment to fuze setting required to decrease the height of burst 10 meters along the trajectory. To increase the HOB, change the sign of the value given in the table.
(5) Change in range per 1-mil change in elevation (Column 5). This is the number of meters change in range, along the gun target line, that would result from a 1-mil change in elevation.
(6) Fork (Column 6). This is the change in the angle of elevation needed to produce a change in range, at the level point, equivalent to 4 probable errors in range.
(7) Time of flight (Column 7). This is the number of seconds needed for the round to travel from the muzzle to the level point at the given elevation. This column is also used to determine the fuze setting for mechanical time fuzes M582 and M577 and variable time fuzes M728 and M732.
(8) Azimuth correction for drift (Column 8). This is the number of mils added to deflection to compensate for the drift of the projectile. Because projectiles drift right when fired, the drift correction will be to the left.
(9) Azimuth correction for a crosswind of 1 knot (Column 9). This is the correction, in mils, needed to correct for a 1-knot crosswind.
b. Columns 10 through 19 list range corrections for muzzle velocity, range wind, air temperature, air density, and projectile weight. These corrections are used in the solution of concurrent and subsequent met. Correction factors correspond to increases or decreases in relation to standard values for muzzle velocity, air temperature, air density, and projectile weight, except the correction factors for range wind. The correction factors for range wind are listed for both head and tail winds. The factors listed assume that all other conditions are standard.
(1) Correction for a 1 meter-per-second decrease or increase in muzzle velocity (Columns 10 and 11). This is a correction to range to compensate for a 1 meter-per-second decrease or increase in muzzle velocity.
(2) Correction for a head wind or tail wind of 1 knot (Columns 12 and 13). This is a correction to range to compensate for a head wind or tail wind of 1 knot.
(3) Correction for a 1 percent decrease or increase in air temperature (Columns 14 and 15). This is a correction to range to compensate for a decrease or increase in air temperature of 1 percent of standard.
(4) Correction for a 1 percent decrease or increase in air density (Columns 16 and 17). This is a correction to range to compensate for a decrease or increase in air density of 1 percent of standard.
(5) Correction for a 1 square decrease or increase in projectile weight (Columns 18 and 19). This is a correction to range to compensate for a decrease or increase of 1 square in projectile weight.
7-9. Extracting Basic HE Data From Table F
Data may be extracted from Columns 1 through 8 of Table F to compute firing data. It is necessary to relate the data extracted to an entry argument. An element of data is said to be a fiction of another element when changes in one of the elements will cause a change in the other.
a. Elevation is a Function of Range. Enter Column 1 with range expressed to the nearest 10 meters, and extract the elevation to the nearest 1 mil from Column 2.
b. Fuze Setting is a Function of Elevation. Enter Column 2 with the elevation expressed to the nearest mil, and extract the fuze setting expressed to the nearest 0.1 of an increment from Column 3 for fuzes M564 and M565. Extract the fuze setting expressed to the nearest 0.1 of a second from Column 7 for fuzes M582 and M577.
c. FS for 10-Meter Decrease in HOB is a Function of Fuze Setting. Enter Column 3 for fuzes M564 and M565 or Column 7 for fuzes M582 and M577 with the fuze setting expressed to the nearest 0.1. Extract the FS expressed to the nearest 0.01 from column 4.
d. D Range for a 1-Mil D Elevation is a Function of Elevation. Enter Column 2 with the elevation expressed to the nearest mil, and extract the change in range for a 1-mil change in elevation expressed to the nearest meter.
e. Time of Flight is a Function of Elevation. Enter Column 2 with the elevation expressed to the nearest mil, and extract the time of flight expressed to the nearest whole second from Column 7.
f. Variable Time Fuze Setting is a Function of Elevation. Enter Column 2 with the elevation expressed to the nearest mil, and extract the time of flight expressed to the nearest 0.1 second from Column 7. Express down to the whole second.
g. Drift is a Function of Elevation. Enter Column 2 with the elevation expressed to the nearest mil, and extract the drift expressed to the nearest 1 mil from Column 8.
7-10. Table G
Table G is the table of supplementary data containing probable error information and certain trajectory elements. For ranges not listed, data can be determined through interpolation. The entry argument for this table is range (Column 1). Elevation corresponding to that range is listed in Column 2 for quick reference. The asterisks extending across the table denote the changeover point from low-angle to high-angle fire. (See Figure 7-16.)
a. Probable Error (Columns 3 through 7). Probable error is defined as the error for a particular charge, and range or elevation that is exceeded as often as it is not exceeded. These errors are based on the standard probability curve and are explained in more detail in Chapter 3.
b. Probable Error in Range to Impact (Column 3). Probable error in range is a value in meters that, when added to and subtracted from the range at the mean point of impact along the gun-target (GT) line, will produce an interval that should contain 50 percent of all rounds fired. PER will vary according to the charge and range.
c. Probable Error in Deflection at Impact (Column 4). Probable error in deflection is a value in meters when applied to the right and left of the mean point of impact, will produce an interval parallel to the line of fire that should contain 50 percent of the rounds fired. PED will vary based on charge and range.
d. Probable Error in Height of Burst (Column 5). Probable error in height of burst is a value in meters which, when added to and subtracted from the expected height of burst, will define an area that should contain 50 percent of the rounds freed. The factors that contribute to PEHB include variations in the functioning of the time fuze.
e. Probable Error in Time to Burst (Column 6). Probable error in time to burst is a value in seconds, which when added to and subtracted from the expected time to burst, will produce a time interval that should contain 50 percent of the rounds fired.
f. Probable Error in Range to Burst (Column 7). Probable error in range to burst is a value in meters which, when added to and subtracted from the expected range to burst, will produce an interval along the line of fire that should contain 50 percent of the rounds fired.
g. Angle of Fall (Column 8). The angle of fall is the value in mils of the least angle measured clockwise from the horizontal to a line tangent to the trajectory at the level point.
h. Cotangent of Angle of Fall (Column 9). The cotangent (cot) angle of fall is the trigonometric function of the angle of fall. When the probable error in range is divided by this factor, the quotient is the vertical probable error. The vertical probable error is the height expected to contain 25 percent of the impacts when firing onto a vertical face.
i. Terminal Velocity (Column 10). The terminal velocity (tml vel) is the speed of the projectile at the level point under standard conditions.
j. Maximum Ordinate (Column 11). The maximum ordinate (MO) is the height of the summit above the origin in meters. This is the height of the trajectory above the howitzer expressed in meters under standard conditions.
k. Complementary Angle of Site for Each Mil of Angle of Site (Columns 12 and 13). This is the correction termed the complementary site factor (CSF) which must be algebraically added to each mil of angle of site to compensate for the nonrigidity of the trajectory. When the CSF is multiplied by the absolute value of the angle of site, the product is the complementary angle of site.
7-11. Table H
a. Table H is used in the solution of concurrent and subsequent met. The extracted value is the correction to range in meters for the rotation of the earth at 0° latitude. A correction for any other latitude is extracted from the small table at the bottom of Table H and is multiplied by the correction from the table. The asterisks extending across the table denote the changeover point from low-angle to high-angle fire.
b. Table H is entered along the left side with the entry range expressed to the nearest 500 meters and along the top or bottom with the exact azimuth (to the nearest mil) to the target (direction of fire) expressed to the nearest listed value. For example, if the azimuth to the target is 1,499 mils, enter Table H with 1400. Whenever the solution determined is exactly halfway between two entry arguments for azimuth to the target use the next higher value. (See Figure 7-17.)
7-12. Table I
a. Table I is used in the solution of concurrent and subsequent met. There are tables for every 10° latitude starting from 0° north or south latitude to 70° north or south latitude. The extracted value is the correction to deflection in mils, for the rotation of the earth. The asterisks extending across the table denote the changeover point from low-angle to high-angle free.
b. Table I is entered along the left side with the entry range expressed to the nearest 500 meters and along the top (for northern latitudes), with the exact azimuth (to the nearest mil) to the target (direction of fire) expressed to the nearest listed value. For example, if the azimuth to the target is 1,499 mils, enter Table I with 1600. For southern latitudes, you enter from the bottom with the exact azimuth (to the nearest mil) to the target (direction of fire) expressed to the nearest listed value. Whenever the solution determined is exactly halfway between two entry arguments for azimuth to the target, use the next higher value. (See Figure 7-18.)
7-13. Table J
a. Table J is used in the solution of concurrent and subsequent met. Data in this table are arranged in 11 columns. Each column lists a fuze setting correction needed to compensate for the effects of nonstandard conditions.
b. The fuze setting used as an entry argument corresponds to the adjusted elevation from a registration (concurrent met) or corresponds to the elevation determined in the solution of a subsequent met. (See Figure 7-19.)
(1) Fuze setting (Column 1). The FS corresponding to the adjusted elevation expressed to the nearest whole increment is the entry argument for Table J.
(2) Correction for a 1 meter-per-second decrease or increase in muzzle velocity (Columns 2 and 3). This is the correction for the FS to compensate for a 1 meter-per-second decrease or increase in muzzle velocity.
(3) Correction for ahead wind or tail wind of 1 knot (Columns 4 and 5). This is the correction to FS to compensate for a head wind or tail wind of 1 knot.
(4) Correction for a 1 percent decrease or increase in air temp (Columns 6 and 7). This is the correction to FS to compensate for a decrease or increase in air temperature of 1 percent of standard.
(5) Correction for a 1 percent decrease or increase in air density (Columns 8 and 9). This is the correction to FS to compensate for a decrease or increase in air density of 1 percent of standard.
(6) Correction for a 1 square decrease or increase in projectile weight (Columns 10 and 11). This is the correction to FS to compensate for a decrease or increase of 1 square in projectile weight.
7-14. Table K
Table K provides corrections to be applied to M564 fuze settings when time fuze M520A1 is being fired. (See Figure 7-20.)
7-15. Illuminating Projectiles
a. Illuminating projectiles are available for the 105-mm and the 155-mm howitzers. They are used to illuminate a designated area for observing enemy night operations, for adjusting artillery fires at night, for marking locations, or for harassment purposes.
b. Illuminating projectiles are base-ejecting projectiles fired with mechanical time fuzes. The filler consists of an illuminating canister and a parachute assembly. The FDO selects the charge to fire, selecting the lowest practical charge to prevent a malfunction caused by the parachute ripping when the flare is ejected from the projectile. The two models of illuminating projectiles for the 105-mm howitzer are the M314A2 and the newer M314A3, which has a slightly longer burning time. The 155-mm howitzer also has two models of illuminating projectiles. These models are the M118 and the newer M485A2, which has a significant increase in illumination time.
NOTE: Data are no longer provided for the M118 projectile. Part 2 of the 155-AM-2 TFT applies to the M485 series only).
c. Part 2 of the 105-mm and 155-mm HE TFT provide data for the illuminating projectile. Most illumination data are provided in a single table. However, TFT may contain additional tables to provide corrections for mechanical time fuzes other than that tabulated in the first table. When more than one table is provided, the tables are identified by letters. The shaded portion of Columns 1 and 2 indicate function during the ascending branch.
(1) Table A. Table A provides firing data and corrections to firing data for illuminating projectiles.
(a) Range to target (Column 1). This is the distance measured from the muzzle to the target on the surface of a sphere concentric with the earth. When range is used as the entry argument for this table, it is expressed to the nearest 10 meters.
(b) Quadrant elevation (Column 2). This is the angle of the tube in the vertical plane. This QE, when used in conjunction with the fuze setting given in Column 3, produces an airburst such that the ignition of the illuminant occurs 600 meters (105-mm is 750 meters) above the level point at the given range.
(c) Fuze setting (Column 3). This is the fuze setting for the M565 fuze. When used in conjunction with the QE given in Column 2, it produces an airburst such that the ignition of the illuminant occurs 600 meters above the level point at the range (105-mm is 750 meters).
(d) Change in QE and FS for an increase of 50 meters in HOB (Columns 4 and 5). These corrections are added to the QE and FS to increase the height of burst by 50 meters. By changing the sign of the correction, the factor is used to lower the height of burst. This factor is also used to correct the QE and FS from Columns 2 and 3 for the VI. These factors must be applied in conjunction with each other.
(e) Range to fuze function (Column 6). This is the horizontal distance from the gun to the point at which the fuze functions.
(f) Range to impact (Column 7). This is the horizontal distance from the gun to the point at which a nonfunctioning projectile will impact.
(2) Table B. Table B provides corrections to fuze setting for mechanical time (MT), M565 to obtain a fuze setting for fuze MTSQ, M577. The corrections are either added to or subtracted from the fuze setting of the MT, M565 fuze to obtain the fuze setting for fuze MTSQ, M577.
7-16. TFT Part 3 and Part 4
Certain TFTs (for example, FT 105-H-7) provide data in two additional parts. Part 3 contains firing data for cartridge, HEP-T, M327 and consists of one table for a single charge. Part 4 contains firing data for cartridge APERS, M546 and consists of one table for a single charge.
7-17. Appendixes
The last portion of the TFT are the appendixes. They contain trajectory charts for HE projectile. Altitude in meters above the origin is plotted against range in meters for every 100 mils of elevation. Time of flight, by 5-second intervals, is marked on the trajectory.
Graphical Firing Tables
To eliminate the difficulties in computing firing data that result from the need to interpolate, the graphical firing table was created. The GFT provides all the information needed to compute firing data in a slide rule form.
7-18. Overview
a. Parts. All GFTs are made in two parts (Figure 7-21). The rule is a rectangular wooden base on which is printed one or more sets of scales. With a few exceptions, GFTs are printed on both sides. The second part of the GFT is the cursor. This is a transparent plastic square that slides on the rule. Engraved in the plastic of the cursor is a manufacturer's hairline used to determine values from the scales.
c. Types. The basic GFT format is the same for all weapons. These formats may be divided into three types: low-angle GFTs, high-angle GFTs, and shell illuminating GFTs.
d. Identification. All GFTs are labeled (Figure 7-22) for identification. The first line of the label on low-and high-angle GFTs indicates the type weapon in bold type; that is, HOW 155mm. Immediately below the weapon type, in smaller print, is the identification of the TFT on which the GFT is based; for example, "155AM2." This is followed by the projectile type and nomenclature, such as "HEM107." The last line of identification of low-angle GFTs tells the charge for which the GFT may be used, such as "CHARGE 4." High-angle GFTs indicate the trajectory "HIGH ANGLE." Shell illuminating GFTs (Figure 7-23) reverse the label with "PROJECTILE ILLUMINATING" on the top and the weapon type on the bottom.
7-19. Low-Angle GFTs
Low-angle GFTs are available for all weapon systems and were developed from the data contained in the TFT of the weapon and projectile. All GFTs are printed with a base scale which represents the data for the base projectile as indicated on the label; that is, "HEM107." One or more ICM/M825 scales may be provided above or below the base scale. The scales are as follows:
a. Drift Scale. This scale, which is printed in black, gives the projectile drift in mils. Since the projectile drifts to the right, the drift correction is always made to the left. Each elevation at which the drift is exactly halfway between the values is printed in red. Artillery expression is applied to determine the value of drift at each of these elevations. In determining drift, it is important to note that drift is a function of elevation. The corresponding portion of the TFT is Table F, Column 8.
b. 100/R Scale. This scale lists the number of mils needed to move the burst laterally or vertically 100 meters at a given range. The numbers on this scale are printed in red. The scale is based on the mil relation formula ( = W/R x 1.0186). 100/R is a function of range. There is no corresponding table in the TFT for 100/R.
c. Range Scale. This scale is the base scale, and all other scales are plotted in relation to it. Range is expressed in meters, The range scale was developed to give as large a range spread as possible, and still permit graduations large enough for accurate readings. Range is read to the nearest 10 meters. The corresponding portion of the TFT is Table F, Column 1.
d. Elevation Scale. This scale is graduated in mils and is read to the nearest mil. The numbers on this scale are printed in red and black. The red numbers denote elevations that are within range transfer limits for a one-plot GFT setting. The corresponding portion of the TFT is Table F, Column 2.
e. Time of Flight/Fuze Setting M582 Scale. This scale lists the time of flight and the fuze settings for time fuzes M582, M577, M728, and M732 corresponding to a given elevation. Time of flight is determined to the nearest whole second. Fuze settings for time fuzes M582 and M577 are determined to the nearest 0.1 fuze setting increment. Fuze setting for fuze VT is determined from the TF/M582 scale by vanishing the tenths and applying a .0. Time of flight and the fuze settings for M582, M577, M728, and M732 are functions of elevation. The corresponding portion of the TFT is Table F, Column 7.
f. Fuze Setting M564 Scale. This scale lists the& e settings for time fuzes M564 and M565. The values are read to the nearest 0.1 fuze setting increment. Fuze settings for M564 and M565 are functions of elevation. The corresponding portion of the TFT is Table F, Column 3.
g. FS/10M HOB Scale. This scale lists the corrections to fuze setting for fuzes M582 or M564 that are needed to raise or lower the HOB 10 meters along the trajectory. FS/10M HOB is a function of fuze setting. The corresponding portion of the TFT is Table F, Column 4.
NOTE: GFTs produced before 1983 include a fork scale. Fork represents the value, in mils, of the change in the angle of elevation needed to produce a change in range of 4 PER at the level point. The corresponding potion of the TFT is Table F, Column 6
h. Met Check Gauge Points. These are red equilateral triangles above the TF/M582 fuze setting scale. The apex of each triangle points to the QE that under standard conditions results in the maximum ordinate of the trajectory passing through a whole line number of a met message. The range and QE at the met check gauge points are preferred for registration aiming points, for met plus velocity error (met + VE) computations, and for determining GFT settings. There is no corresponding table in the TFT.
NOTE: Chapter 10 explains registrations and determining GFT settings, and Chapter 11 explains met + VE computations.
i. Height-of-Burst Probable Error Gauge Points. These gauge points appear on some GFTs above the fork scale or on the M564 fuze setting scale. They are red right triangles and indicate the range and fuze settings at which the PEHB is 15 meters. Larger HOB dispersion must be expected when time fuzes are used with a particular charge at ranges exceeding the gauge point. Some charges have two such gauge points. The one on the left of the GFT indicates the range at which the PEHB for the next lower charge is 15 meters. The PEHB can be determined from Table G, Column 5, of the TFT.
j. Range Probable Error Gauge Point. This is a black equilateral triangle located above the FS/ 10M HOB scale. It indicates the range at which the range probable error equals 25 meters. Ranges to the left of the gauge point have a PER of less than 25; ranges to the right of the gauge point have a PER of greater than 25. The PER can be determined from Table G, Column 3, of the TFT.
k. Range K and Fuze K Lines. These are based on data derived from computer simulations of artillery firing. The computer program uses 50 sets of weighted nonstandard conditions of temperature, density, range wind, and muzzle velocity. Firing simulations were made by using these 50 sets of nonstandard conditions for each of a number of ranges within the range limits for each charge. Every group of 50 firings for each range provided data to calculate a total average range correction (range K) and total average fuze correction (fuze K) for that particular range. These values of range K and fuze K were graphically plotted versus the corresponding range for all simulated ranges for each charge. These curves were simplified as tight line approximations and were used to create the data to construct the range K and fuze K lines on the GFT. These approximations were considered to be acceptable, up to the point where no more than 1 PER was introduced. This acceptable range area is denoted on the GFT by the elevation numbers printed in red. Those numbers corresponding to an error larger than 1 PER are printed in black. From this is derived the range transfer limits for a one-plot GFT setting. The range K and fuze K lines are ignored for multiplot GFT settings.
l. Improved Conventional Munitions Scales. These scales are on some graphical firing tables. They are located above the DEFL CORR/DRIFT scale. The scales apply to a specific type of ammunition as indicated by the model number at the left end of the scale.
(1) DEFL CORR. This is the top scale on GFT ICM scales. This scale incorporates base scale drift and the ballistic correction as tabulated in Table A of the appropriate addendum.
(2) QE. The next scale (the top scale on older GFTs) is the quadrant scale. This scale provides the quadrant to fire for the ICM projectile. The ICM quadrant is read to the nearest mil by placing the manufacturer's hairline over the base scale quadrant and reading up under the MHL to the appropriate ICM quadrant scale. This QE incorporates the ballistic correction given in Table A of the appropriate addendum.
(3) FS. The last scale provides the fuze setting to fire on the ICM projectile. The ICM FS is read to the nearest 0.1 increment by placing the MHL over the base scale FS and reading up under the MHL to the appropriate ICM FS scale. This FS incorporates the ballistic correction given in Table B of the appropriate addendum.
7-20. High-Angle GFT
a. High-angle fire is delivered at elevations greater than the elevation corresponding to the maximum range for a charge. All howitzers can deliver high-angle fire effectively.
b. The high-angle GFT consists of one rule with ballistic data for multiple charges on each side. The scales on the high-angle GFT from top to bottom are as follows:
(1) 100/R. This scale lists the number of mils needed to move the burst laterally or vertically 100 meters at a given range. The scale increases from right to left, is read to the nearest mil, and applies to all charges. There is no corresponding portion in the TFT.
(2) Range. The range scale is expressed in meters and applies to all charges appearing on that side of the GFT. Range increases from left to right and is read to the nearest 10 meters. The corresponding portion of the TFT is Table F, Column 1.
(3) Elevation. Elevation is expressed in mils and increases from right to left. It is visually interpolated to the nearest mil. The corresponding portion of the TFT is Table F, column 2.
(4) 10-Mil site factor. The values on this scale denote the site for each 10 mils of angle of site. The numbers are printed in red and are negative values. This factor actually reflects the complementary angle of site for a positive VI. Consequently, a slightly more accurate solution for negative angles of site can be determined from the TFT. Because of the minimal effect of site in high-angle fire, these values are acceptable for both a positive and negative VI. The scale increases from left to right and is read to the nearest tenth (0.1) of a mil. There is no corresponding portion in the TFT.
(5) Drift. The values on this scale are in mils. The scale increases from right to left and is read to the nearest mil. The corresponding portion of the TFT is Table F, Column 8.
(6) Time of flight. This scale is graduated in seconds and is used to determine both time of flight (to the nearest whole second) and VT fuze setting (to the next lower whole second). The scale increases from right to left. The corresponding portion of the TFT is Table F, Column 7.
NOTE: Because the scales increase in different directions, the computer must be careful in reading the high-angle GFT. The elevation, 100/R, drift, and TF scales increase from right to left. The range and 10-mil site scales increase from left to right
7-21. Illuminating Projectile GFT
Graphical firing tables have been developed for use with all 155-mm M485A2 illuminating projectiles and with the 105-mm M314A1, M314A2, and M314A3E1 projectiles. Illumination scales are provided for enough charges to cover the spectrum of range for the shell and weapon.
a. 100/R. This scale is printed along the top edge of the GFT. For a given range, the 100/R scale denotes the number of mils needed to shift the burst 100 meters laterally or vertically. The 100/R is read to the nearest mil. There is no corresponding portion in the TFT.
b. Range. The range scale is the base scale of the illuminating GFT. All other scales are plotted with reference to the range scale. Range is read to the nearest 10 meters. The corresponding portion of the TFT is Part 2, Table A, Column 1.
c. Elevation to Impact. This scale is graduated in mils. Low-angle elevation increases from left to right and is read to the nearest mil. The scale is used to determine the range (on the range scale) to which a nonfunctioning projectile will impact. There is no corresponding portion in the TFT.
d. Height of Burst. These scales are graduated in 50-meter increments. The HOB is determined by expressing the VI to the nearest 50 meters and algebraically applying the VI to the optimum HOB. There is no corresponding portion in the TFT.
e. QE. The QE scale shown for each listed height of burst gives the QE needed to achieve the height of burst at the desired range. The scale is graduated in mils and is visually interpolated to the nearest mil. A heavy black arrow on the QE scale indicates the part of the trajectory that is at or near the summit and that does not exceed by 50 meters the height of burst that it represents. (See Figure 7-24.) The corresponding portion of the TFT for a 600-meter (750 meters for 105 mm) HOB is Part 2, Table A, Column 2.
f. FS M565. This scale consists of a series of red arcs. The scale includes a red line for each whole fuze setting increment for the MT, M565 fuze. The value of each line is printed in red at the bottom of the scale. The fuze setting is read for the desired range and HOB to an accuracy of 0.1 FS increment by visual interpolation. The corresponding portion of the TFT for a 600-meter (750 meters for 105 mm) HOB is Part 2, Table A, Column 3.