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Figure SI. Inserting the headspace gage.

Figure SI. Inserting the headspace gage.

insert the NO GO end of the gage; if it does not enter correct headspace is set. Remember, to unscrew the barrel, or to screw the barrel into the barrel extension, the lug on the barrel locking spring must be alined with the %-inch hole in the right side plate (para lb.).

(6) If the NO GO end of the gage enters the T-slot, headspace is too loose. The barrel must be screwed into the barrel extension (one click at a time) checking with the gage after each click, until the GO end enters and the NO GO end does not.

(7) Remove the gage. 12. Timing a. General. Timing is the adjustment of the weapon so that firing takes place when the recoiling parts are between .020 and .116 inches out of battery to prevent contact between the front end of the barrel extension and the trunnion block. Timing is correctly set when the following conditions are met:

(1) The recoiling parts are locked together.

(2) Firing takes place just before the parts are in battery (fully forward).

(3) When the gun fires on the FIRE gage, and does not fire on the NO FIRE gage. Timing must be checked and/or set each time headspace is set, or whenever timing is questionable.

b. Checking and/or Setting Timing.

(1) Insure that the gun has correct head-space adjustment.

(2) Cock the gun; pull the retracting slide handle all the way to the rear and return it to its most forward position. Press the bolt latch release and allow the bolt to go forward.

Note. Do not depress the trigger.

Figure 8S. Rotating the timing adjustment nut to the left

(3) Raise the extractor and pull the retracting slide handle back until the front end of the barrel extension is about one-fourth of an inch from the trunnion block.

(4) Insert the NO FIRE timing gage between the barrel extension and the trunnion block, placing the beveled edge of the gage on the barrel notches (fig 82).

(6) Let the barrel extension close slowly on the gage.

(6) Depress the trigger firmly, attempting to release the firing pin. The firing pin should not release. If the firing pin does release, the gun is timed to fire too early.

(7) To correct for this, pull the retracting slide handle to the rear, allow the bolt to go forward. Insert the fire gage, remove the backplate and screw the timing adjustment nut to the left until it rests on the trigger lever (fig 83). Press "up" firmly on the trigger lever attempting to fire. Rotate the timing adjustment nut to the right one

(1) notch at a time, each time pressing up firmly on the trigger lever, attempting to fire the weapon.

(8) When the firing pin is released, turn the timing adjustment nut two (2) additional notches to the "right" and replace the backplate.

Caution. Do not attempt to cock the gun with the backplate off.

(9) Recock the weapon and allow the bolt to go forward. Insert the "NO FIRE" gage between the trunnion block and the barrel extension and attempt to fire the weapon by depressing the trigger. The weapon should not fire. If the weapon does fire, a mechanical defect exists and the gunner should notify his organizational maintenance personnel.

(10) Replace the "NO FIRE" gage with the "FIRE" gage and attempt to fire. The weapon should fire.

(11) When all of the above procedures have been completed, the weapon is correctly timed.

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  • Robert
    Why do you turn the timing nut two additional clicks when timing the m2 .50 cal?
    9 years ago

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