Figure 153. Chart 5. bulUt drop verwu» range.
121 Field expedient. Thin method may be lined when the time or the situation does not permit the use of the known distance. It in mostly used for confirm in* old zeroes. The firer will require an observer equipped with binoculars or a spotter telescope to As«i*t him. The firer and observer pick out an aiming point in the center of an area— hillside, brick house, or any surface where the strike of the bullet can be observed. The range to this point can be determined by map survey, the range card of another weapon, or by ground measurement- Once the firer has annum ed a stable position, the observer must position himself to the rear of. but close to. the firer. The observer's binoculars or telescope should be positioned approximately 4.> to M> rentimeter* (18 to 24 inchest above the weapon end directly in line with the axis of the lM>re. Positioning his optics in this manner enables the observer to see the truce <>f the bullet as it moves down range. The trace or »hock wave of the bullet sets up an air turbulence sufficient enough to be observed in the form of « vapor trail. The trace of the bullet enables the observer to foliothe path of the bullet in it* trajectory toward
¡U impact area. The trace will disappear prior to impact making it appear to the inexperienced observer that it struck above or beyond its actual impact point. For example» at 300 meterá the trace will disappear approximately IS centimeters above its impact point. At 500 meters the trace will disappear approximately 63 centimeters above its impact point. Wind causes lateral movement of the bullet. This lateral movement will appear as a drifting or bending of the trace in the direction that the wind is blowing and must be considered when determining windage zero. The observer must be careful to observe the trace at its head and not be misled by the bending tail of the trace in a stout cross wind. Prior to firing the first round, the firer must set his sights so that he will hit on or near his aiming point. This sight setting is based on the old zero or an educated guess. The firer fires a shot and gives a call to the observer. If the strike of the bullet could not be observed, the observer gives a sight adjustment based on the trace of the bullet. Once the strike of the bullet can be observed in the desired impact area, the observer compares the strike with the call and gives sight adjustments until the bullet impact coincides with the aiming point.
b. Confirming Zero.Once a rifle has been zeroed, and it becomes necessary to confirm this zero for any reason, it can be zeroed again by firing at a known distance with the sights set on the old zero. If a sight adjustment is necessary to hit the aiming point, this zero change will remain constant at all ranges. For example, if firing at a distance of 500 meters with the old zero and it becomes necessary to raise the elevation 3 clicks to hit the aiming point, the elevation zero should be raised 3 clicks at all ranges.
c. Zeroing the Sniper Rifle Using the Scope Sight. The most precise method of zeroing the sniper rifle, utilizing the scope sight, is to fire and adjust the sight to hit a given point at 300 meters. The following zeroing procedure should be utilized:
III Properly mount the scope on the rifle.
12) Select or prepare a distinct target (aiming crossl at 300 meters Ifig 1541.
13) Assume the supported prone position.
Loosen the power ring lock by turning the knurled nut counterclockwise.
151 Turn the power adjustment ring to the low power range setting 13 index I.
161 While aiming, superimpose the crosshair over the aiming cross and position the 76-cm (34 in I target between the vertical stadia marks.
171 Fire a 3-round group and determine ita location and distance from the aiming cross.
(8) Utilizing the elevation and windage rule determine the number of clicks minutes* of elevation and windage necessary to move the center of the group to the center of the aiming cross.
Remove the elevation and windage turret caps and make the necessary sight adjustments. In making flight adjustments, remember to turn the adjusting screws in the direction you wish to move the strike of the bullet or group.
1101 Fire additional groups as necessary to insure that the center of the shot group coincides with the point of aim at 300 meters.
Oil Zero the elevation and windage scales and replace the turret caps.
113» To engage targets at other ranges the firer need only set the desired range <300 to 900 meters, inscribed on the focusing ring I opposite the reference clot on the top of the scope. To engage targets at undetermined ranges the firer ranges on the target: in conjunction with ranging, elevation is imparled to the »cope by the ballistic cam; thia compensate» for trajectory.
No*4. Do not move th* •t«Y«tkm and wlndsfs ad-juitlnf icrcwa beyond the point wbwra mid* raovwntnt «topi. The mcchanlim may becoma ditefliafad and require factory «pair.
114) The ballistic cam principle of the sight eliminates the necessity to adjust the sights manually for each range, or to record aero settings. However, for ease of correction, to facilitate minor changes in elevation or windage, or to indicate a mechanical zero for the 300-meter seroing range, the elevation and windage scales should be zeroed once the 300-meter zero is established. This is accomplished by rotating the movable index scale nntil the 0 is alined with the adjusting screw index line.
d. Firing at Targets for Which No Definite Zero Has Been Established. When firing on targets at a range of 100 meters or less, the 100-meter zero should be used. The difference between the impact of the bullet and the aiming point is negligible. The difference between the impact of the bullet and the aiming point increases as the range increases, if the lights are not moved. If a firer s zero is 46 clicks at 900 meters and 40 dicks at BOO metera, and if he estimates the range of a target at 850 metera, he should use a sight setting of 43 clicks rather than using his BOO- or 900-meter zero or the adjusted aiming point method. At any range, moving the sights is preferred over the adjusted aiming point method.
e. Range Estimation Using Telescopic Sight. The optical sight has one set of vertical and one set of horizontal stadia lines. When used at a range in hnndreds of meters corresponding to the power setting, the stadia lines on the vertical crosshair measure a height of 76 cm (30 in) and the lines on the horizontal crosshair a width of 1S2 cm <60 in). To utQize the stadia lines the firer determines a 76 cm high target (approximately the distance from a man's groin to the top of his head) and adjusts the power ring on the scope until the stadia lines just bracket the target (fig 134). The ballistic cam of the scope will simultaneously adjust for the range and the firer is ready to engage the target.
/. Use of Record Data Sheet.
111 During the zeroing period there are several items of information to be recorded by the firer. Included in this recorded data is a record of each shot or shot group fired, and the weather conditions and their effects on the strike of the bullet and the firer. If used properly It will provide the necessary information for initial sight settings at each distance or range. It provides a basis of analyzing the performance of the firer and his rifl«( and it is a valuable aid In making bold and accurate aight changes.
(2) A sample record data sheet is pictured in figure 155. This sample record data sheet or something similar can be made by the individual or mimeographed. This sheet, when properly maintained, will give the firer, or Instructor, a complete picture of the firer's performance and zero under varying weather conditions. The individual firer should use a new record data sheet for each different weapon and include data on the placa, ammunition lot, firing position, distance, and weather conditions.
(3) Instructions in the use of the record data sheet should be given prior to zeroing. The following procedure should be used for filling out and maintaining the record data sheet. This sheet is maintained in three phases: before firing, during firing, and after firing.
(a) Before firing.
Place: Name of range or location.
Ammunition: Type and lot number. Temperature:
Position: Firing position used. Distance: Range to target In meters. Elevation: Elevation in minutes to be used for initial shot (with the hooded aperture in the up position add Vi f.
(b) During firing.
Call: Place a dot in the call block where that shot is expected to hit. If excessive movement is seen as the rifle fires, indicate the direction of movement with an arrow in the call block.
Hit: Plot location of shot group bjr number in target after shot or group is marked.
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