FM-3-09 Fire Support and Field Artillery Operations Download
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Appendix C C-8 FM 3-09 30 April 2020 MEASURING AN AZIMUTH USING THE RECIPROCAL LAYING METHOD C-40. Reciprocal laying is a procedure by which the 0-3200 line of one instrument and the 0-3200 line of another weapons on the azimuth of fire. The aiming circle is used to measure horizontal clockwise angles from the line of fire instrument are laid parallel. C-41. The aiming circle is the primary means by which the cannon battery orients weapons on the azimuth of fire. The azimuth of fire is the direction, expressed in mils, that a fire unit is laid (oriented) on when it occupies a position (ATP 3-09.50). The aiming circle is used to measure horizontal clockwise angles from the line of fire to the line of sight to a given aiming point. In reciprocal laying, the aiming point for the aiming circle is the howitzer panoramic telescope. C-42. Survey may not be available. To establish directional control and lay units by the orienting angle method, the orienting line must be established. Without survey, the orienting line can be established by hasty survey techniques. Once the orienting line is established, the steps shown above apply. The OS grid location and altitude may be obtained by GPS, map spot or by hasty traverse. If survey data is not available and hasty survey is not possible, then the next best method is laying by grid azimuth. C-43. In reciprocal laying, the 0-3200 line of one instrument and the 0-3200 line of another instrument are laid parallel. ACCURATE WEAPON AND AMMUNITION INFORMATION C-44. Accurate weapons and munitions information is developed and provided by firing units, FDCs, and sustainment cells. The weapon information is normally applied automatically using the AFATDS. If the AFATDS is not functioning the procedures to apply weapons information manually is found in the applicable technical manuals and tabular firing tables. Firing tables and technical gunnery procedures allow the unit to consider specific ammunition information as follows: Weight of the projectile. Type of fuze used. Muzzle velocity variations. Propellant temperature. C-45. Weight of the projectile affects how far or short the round will travel. If the round is heavier than standard it will have a decreased range, the opposite is also true if the round is lighter than standard it will have an increased range. Compensation for projectile weight is found in the appropriate tabular firing table that is being used. C-46. The type of fuze will determine the information that is set for the fuze. For a point detonating fuze no information is set on the fuze and the round will function as it hits a solid target. Variable time fuze can set function at 7 meters above the ground by setting the fuze for the appropriate range to be used. Time fuzes can be set at various heights above the ground to have better effects against soft targets, such as dismounted infantry, radars, C2 systems, or fuel points. All these fuzes require different settings based on their type, function, and ranges to be used. C-47. Muzzle velocity variation is the difference from a standard speed the round departs the barrel with. If the round is traveling faster than the standard speed it will have an increased range, the inverse is also true if the round is traveling slower when it leaves the barrel it will have a decreased range from standard. We measure this with the M90 chronograph or the M94 muzzle velocity system using the appropriate technical manual. While it is not practical to predict (within ±0.1 m a second) the velocity of every round, it is possible to approximate velocities to within ±1 or ±2 m a second with current available information. This may be useful when calibration is not possible, when updating calibration data, or when trying to increase the accuracy of inferred muzzle velocity techniques. When calibration is not possible, the shooting strength of the howitzer can be used as the muzzle velocity variation. While this may be enough when no other data are available, it is important to understand that a muzzle velocity variation consists of more than just shooting strength. An equation can be created for determining a muzzle velocity variation by using its basic parts. In the event the muzzle velocity system becomes inoperable the unit can register or extract powder efficiency data from another system to apply to the inoperable muzzle velocity system weapon's shooting strength data.