Bore Sighting The M109-series Howitzer

CANNON CREW MEMBER MOS 13B SKILL LEVELS 1 AND 2 BORESIGHTING THE M109-SERIES HOWITZER SUBCOURSE FA 3330-B Reviewed by SSG Warren T. Davis (Oct 04) US Army Field Artillery School Fort Sill, Oklahoma DSN: 442-3300 Three Credit Hours GENERAL This subcourse is designed to train the skills necessary for performing tasks related to boresighting the panoramic and elbow telescopes by using the following methods: test target, distant aiming point, and checking boresight with the M140 alignment device. This subcourse is presented in one lesson corresponding to a terminal objective supporting the following soldier's manual tasks: TASK NO: 061-270-1214 TASK:

Boresight the direct fire telescope (M109A5).

CONDITIONS: You will be given an M109-series howitzer in a firing position, and section equipment STANDARDS: Boresight within 2 minutes IAW TM 9-2350-311-10. TASK NO:

061-266-2005

TASK:

Boresight the Panoramic Telescope by using a Distant Aiming Point (DAP)

CONDITIONS: You will be given a howitzer in a field location, section equipment, and a DAP. STANDARDS: Boresight to 0 mils within 2 minutes IAW TM 9-1015-234-10, or TM 9-2350-311-10. TASK NO:

061-266-2239

TASK:

Check the Boresight of the Panoramic Telescope with the M139 or M140 Alignment Device.

CONDITIONS: You will be given a howitzer in a field location, a M139 and M140 Alignment devices. STANDARDS: Verify the Boresight within +/_ 0.5 mils within 2 minutes IAW TM 9-1015-234-10, or TM 9-2350-311-10.

TABLE OF CONTENTS Section Lesson: Boresight the Pantel and Elbow Telescope on the M109-series Howitzer (M109A6 Paladin does not have an elbow telescope). Introduction Checking Boresight of the Panoramic Telescope with the M140 Alignment Device Preparations for Boresighting with the Test Target Boresighting the Panoramic Telescope and Direct Fire Telescope with the Test Target Preparation for Boresighting with a Distant Aiming Point Boresighting the Panoramic Telescope and Direct Fire Telescope with a Distant Aiming Point Summary EXAMINATION

LESSON BORESIGHT THE PANTEL AND ELBOW TELESCOPE ON THE M109-SERIES HOWITZER OBJECTIVE After completing this lesson, you will be able to boresight the pantel and elbow telescope by using a test target and distant aiming point. You also will be able to check boresight with the M140 alignment device. REFERENCES This lesson is based on TM 9-2350-311-10 and other materials approved for US Army field artillery instruction; however, development and progress render the text continually subject to change. Therefore, base your examination answers on material presented in this lesson rather than on individual or unit experience. 1. INTRODUCTION. Boresighting procedures ensure that the panoramic telescope (pantel), direct fire telescope, and tube are in alignment with each other. Boresighting is an important element in aiding the howitzer section to deliver accurate fire. The howitzer should be boresighted-• Any time the sight has been subjected to any shock other than firing. • Any time the howitzer fires inaccurately for no apparent reason. The two methods of boresighting the M109-series howitzers are as follows: • Test target (TT). • Distant aiming point (DAP). The M140 alignment device is used to check boresight. NOTE: The newer M140A1 is battery operated and is not fielded Army wide yet, refer any questions that are in the examination to the M140 Tritium version. 2. CHECKING BORESIGHT OF THE PANORAMIC TELESCOPE WITH THE M140 ALIGNMENT DEVICE. Using the M140 alignment device is the most convenient method to check boresight of the howitzer. It can be used in almost any location and can be used at night as easily as during daylight hours. To check boresight of the M117-series panoramic telescope, use the following procedures: WARNING THE M140 ALIGNMENT DEVICE USES RADIOACTIVE TRITIUM GAS (H-3) TO PROVIDE A LIGHT SOURCE. IF A LEAK DEVELOPS, THERE WILL BE LITTLE OR NO LIGHT. TREAT THE DEVICE AS DANGEROUS MATERIAL. DO NOT ATTEMPT TO REPAIR IT. a. Remove the alignment device from its stowed position. In a low-light area, check the alignment device for illumination. If illumination is weak or there is no illumination, take the following precautions:

• Double bag (plastic bag) the device, put a tag on it. • Decontaminate any exposed skin area with nonabrasive soap and water. • Notify your Chain of Command, RPO, or Safety Officer of the possibility of radioactive contamination. b. Next, remove the protective cover from the dovetail adapter located on the left side of the tube (Figure 1). Inspect the adapter for nicks or burrs. If any exist, notify organization al maintenance. Install the alignment device on the dovetail adapter (Figure 2).

NOTE: Use Figure 3 below to help you locate the parts of the pantel and mount you must use in boresighting.

c. Set the gunner's aid counters to 0. Rotate the pitch knob (Figure 4, A) clockwise or counterclockwise until the bottom end of the left gear sector arc B is flush with the adjoining casting C. The view in Figure 5 shows the arc after it has been adjusted.

d. Rotate the crosslevel knob (Figure 5) until the right end of the top gear sector arc is flush with the adjoining casting. The view in Figure 6 shows the arc after it has been adjusted.

e. Next, align the scribe lines on the pitch and cross-level knobs. Figure 7 illustrates the pitch and cross-level knobs aligned and not aligned.

NOTE: When you have adjusted the top and left arcs and aligned the pitch and cross-level knobs on the scribe lines, the mount is in alignment. If the mount is not in alignment, you cannot fully see the M140 alignment device through the pantel eyepiece. If there is excessive cutoff due to incorrect alignment, the M140 alignment device may not be seen at all through the pantel eyepiece. NOTE: To verify boresight with the M140 alignment device, the pantel mount must be scribed. If your howitzer does not have these scribe lines, you must scribe the mount. This is done by following the procedures listed in TM 9-2350-311-10 for leveling the trunnions and scribing the mount. f. Verify boresight using the M140 alignment. Before boresighting the M109 howitzer you should check boresight using the M140 alignment device; by doing this you may find that your weapon may not need to be adjusted. To verify the boresight of your howitzer with the M140 alignment device, refer to Figures 1 through 8 in this lesson. Before starting, zero the tube using the tested gunner's quadrant; then you must align the scribe lines on the cross-level knob and pitch knob of the M145 mount. Rotate the pitch knob and crosslevel knob in a clockwise direction; the position of the knobs will be correct when the upper end of the gear sector driven by the pitch knob and the right end of the arc driven by the cross-level knob are nearest to the flush position. Align the pantel reticle with the M140 alignment device reticle (Figure 9); the azimuth counter should read 3200 ± 0.5 mils.

g. If the reading on the pantel is not 3200 ±0.5 mils, then to verify that the M140 alignment device is or is not defective or that your weapon is or is not out of boresight, you must run a comparison test. A comparison test is simply checking boresight with two additional M140 alignment devices. PRACTICE EXERCISES: Complete the following exercises by circling T for true F for false, circling the letter preceding the correct answer, or filling in the blanks, as appropriate. Be sure to complete the practice exercises as they appear. They are "building blocks" and will help you complete the rest of the subcourse successfully. The answers follow the last exercise. If any of your answers are incorrect, restudy the appropriate part of the subcourse before you continue. 1. How many M140 alignment devices does it take to do a comparison test on the pantel? a. b. c. d.

two three four six

2. What is the purpose of the M140 alignment device? a. b. c. d.

to verify the azimuth of fire to verify the howitzer has correct data to verify the azimuth of lay to check the boresight of your howitzer

3. What is the allowable error on the M140 alignment device? a. b. c. d.

±0.5 ±1.5 ±2.5 ±5.0

4. At what quadrant elevation should the tube be placed before verifying boresight using the M140 alignment device? a. b. c. d.

300 100 50 0

ANSWERS: 1. b 2. d 3. a 4. d 3. PREPARATIONS FOR BORESIGHTING WITH THE TEST TARGET. Some preparation is required before the howitzer is boresighted by using the test target. a. First, the tube must be prepared. To do this, open the breech and install the breech boresight disc in the tube (Figure 10).

If you do not have a breech boresight disc, the obturator spindle vent may be used as a rear sighting guide. It is not as accurate, but it will work. If the vent is used, you must close the breech and open the firing lock to expose the vent. To complete preparing the tube for boresighting, you must properly place the cross hairs on the front of the tube. Figure 11 illustrates the proper method of installing the cross hairs.

Thread one cross hair through the top and bottom holes A of the muzzle brake. Make sure the vertical hairline is aligned on the witness marks. Align the horizontal cross hair with the witness marks B at the end of the tube. Pull the cross hair tight, and secure it with tape. The tube is now ready for boresighting. b. Next, the trunnions must be as level as possible, but no more than 90 mils cant. There are two methods. (1) For the first method, follow these steps as follows: • Obtain a gunner's quadrant that has been checked by the micrometer test and end-for-end test (see your -10 TM for these procedures). • Set the gunner's quadrant index arm and micrometer to 0. • Set the quadrant on the crosswise leveling pads. • Traverse the howitzer until the bubble in the gunner's quadrant centers. (2) An alternate method is to use the scribe lines on the M15 quadrant. To use this procedure, do the following: • Carefully align the scribe lines (Figure 12) on the quadrant.

• Set 0 mils elevation on the quadrant. Level the elevation bubble by elevating or depressing the tube. • Have someone slowly traverse the tube manually while you watch the cross-level bubble. At some point, the cross-level bubble will center. Stop traverse, level the tube, and center the elevation bubble. • Recheck the cross-level bubble, and recenter it if necessary. When the elevation bubble is centered and the cross-level bubble is exactly centered, the trunnions are level. c. With the tube prepared and the trunnions level, the last step in preparing to boresight is to set up the test target. Figure 13 illustrates a test target with measurements on it. Yours will not have these measurements on it. The measurements are given in case you need to make a test target.

Set the test target on a tripod or some other stable but movable stand. Locate the test target at least 50 meters in front of the tube. Align the cross hairs of the muzzle with the center aiming diagram of the test target by moving the test target. Do not move the tube. Figure 14 shows the tube cross hairs properly aligned on the center aiming diagram of the test target.

When these preliminary steps are completed, the weapon is ready to be boresighted. PRACTICE EXERCISES: 5. The two methods of boresighting are-a. b. c. d.

pantel and M140 alignment device. distant aiming point and M140 alignment device. distant aiming point and test target. distant testing target and alignment point.

6. If you do not have a breech boresight disc, you may sight through the-a. elbow telescope. b. obturator spindle vent. c. firing lock. 7. When leveling the trunnions, the tube must be at ____ mils elevation. 8. The cross hairs on the tube are aligned on the ____ aiming diagram of the test target. ANSWERS: 5. c. 6. b. 7. 0 8. center 4. BORESIGHTING THE PANORAMIC TELESCOPE AND DIRECT FIRE TELESCOPE WITH THE TEST TARGET. a. To boresight the panoramic telescope with the test target, you must use the proper aiming diagram (butterfly) on the test target. (1) Level the mount first. As before, use the pitch and cross-level knobs to center the bubbles in the level vials. Set the gunner's aid counter to 0. Next, use the azimuth and elevation knobs to precisely align the pantel cross hairs on the left aiming diagram on the test target (Figure 15).

(2) Check to see that the muzzle cross hairs are still centered on the middle aiming diagram and the pantel mount is still in alignment. The azimuth counter should read 3200. If the azimuth counter does not read 3200, remove the detent shaft cover and depress and rotate the detent shaft until 3200 appears in the azimuth counter window. Recheck the sight picture. Replace the detent shaft cover. The pantel is now boresighted. b. To boresight the elbow telescope (direct fire telescope) by using the test target, use the azimuth and elevation knobs to align the elbow telescope reticle pattern on the right aiming diagram of the test target. Figure 16 shows the proper aiming diagram and reticle alignment.

Set telescope mount slip scales A and B to elevation (4) and azimuth (4) (Figure 17). Be careful not to move azimuth knob or elevation knob when setting slip scales. The elbow telescope is now boresighted. NOTE: The test target can be used to boresight at night if it is prepared beforehand. To do this, drill a 1/16-inch hole in the exact center of each of the three aiming diagrams. Cover the holes with a piece of cloth stapled to the back of the test target. When boresighting at night, hold a flashlight against the material of the appropriate aiming diagram.

PRACTICE EXERCISES: Enter the letter of the correct aiming diagram (Figure 18) to be used to align each item listed below. 9. ___Tube 10. ___Pantel 11. ___Elbow telescope

ANSWERS: 9. B 10. A 11. C 5. PREPARATION FOR BORESIGHTING WITH A DISTANT AIMING POINT. To boresight by using a distant aiming point, you must prepare the tube in the same manner as for using the test target, except for the last step. Traverse the tube to the distant aiming point. The distant aiming point should be easily identifiable and at least 1,500 meters from the howitzer. Align the vertical cross hair of the tube exactly along the left edge of the distant aiming point, and elevate or depress the tube to align the horizontal plane of the point (Figure 19).

6. BORESIGHTING THE PANORAMIC TELESCOPE AND DIRECT FIRE TELESCOPE WITH A DISTANT AIMING POINT. To boresight the pantel and elbow telescope, use the procedures discussed previously. On the pantel, use the azimuth and elevation knobs to align the cross hairs on the distant aiming point. Reset the azimuth counter to 3200 if necessary. To boresight the elbow telescope, use the azimuth and elevation knobs to align the reticle on the distant aiming point. Reset the slipping scales to (4). Figures 20 and 21 show proper alignment of the pantel and elbow telescopes.

PRACTICE EXERCISES: 12. At what distance, in meters, must the distant aiming point be? a. b. c. d.

1,150 1,500 2,100 2,500

13. After you have aligned the pantel on the distant aiming point, the azimuth counter should read-a. b. c. d.

2400. 2800. 3200. 3400.

14. After the elbow telescope is boresighted, you must reset the slipping scales to-a. b. c. d.

(4). (5). (6). (7).

ANSWERS: 12. b. 13. c. 14. a.

7. SUMMARY. Boresighting is an important element in aiding the howitzer section to deliver accurate fire. Boresighting should be done as soon as possible after occupation of a new position. Either of the two methods discussed, test target or distant aiming point, will work equally well. The method used will depend on the situation. Extreme care must be used to ensure the boresight is as accurate as possible. The M140 alignment device is a quick check to see if the weapon needs to be boresighted.