1. Retract the recoiling parts enough to remove the FIRE gauge. Allow them to return forward into the battery.

2. Remove the backplate assembly. (See fig. 13-34.)

3. Locate and turn the trigger bar adjusting nut one notch to the right (fig. 13-53).

4. Reinstall the backplate assembly. (See fig. 13-46.)

5. Retract the recoiling parts enough to insert the FIRE gauge again. Allow the barrel extension to close on the gauge slowly.

Figure 13-54.-MK 19 MOD 3 40-mm machine gun.

6. Depress the trigger. The firing pin should release.

If necessary, repeat the procedure until the firing pin releases with the FIRE gauge installed.

Early Timing Adjustment.- If the timing of the gun is early, the firing pin will release with the NO-FIRE gauge installed. The adjustment procedures for this situation are the same as those described above. However, turn the trigger bar adjusting nut one notch to the left. Reinstall the NO-FIRE gauge and depress the trigger. The firing pin should not release. Repeat the procedure as necessary.

The importance of obtaining the correct headspace and timing adjustments on the .50-caliber BMG cannot be stressed enough. The U.S. Army field Manual (FM23-65) and appropriate MRCs for the weapon describe the required procedures in detail. Consult those References to make these adjustments. Do them carefully and deliberately.