Figure 13-50.---Checking the headspace with the GO end of the
Figure 13-49.--Headspace and timing gauge set.
4. Retract the bolt slightly, not exceeding 1/16 inch
(fig. 13-50). Recheck the headspace adjustment as
gauge. The following steps explain how to check and set
the headspace adjustment:
If necessary, repeat this procedure to obtain the
1. With the cover group closed, cock the gun. Do
proper adjustment. Be sure to unscrew the barrel only
so by pulling the retracting slide handle all the way to
one notch (click) each time. If the adjustment cannot be
made within one to five (maximum) notches (clicks),
2. Depress the bolt latch release and slowly ease
notify the maintenance supervisor.
the restricting slide handle and bolt all the way forward.
Headspace Too Loose.-- If the headspace is too
3. Raise the cover group. Pull back on the
loose, the NO-GO end of the gauge will enter the T-slot
retracting slide handle slightly. Move the bolt not more
freely. The adjustment procedures for this situation are
than 1/1 6 inch to the rear. That prevents the driving
the same as those just described. However, screw the
spring group and the weight of the parts from giving a
barrel in one notch (click) at a time for each adjustment
false reading. Raise the extractor.
4. Insert the GO end of the headspace gauge into
TIMING ADJUSTMENT.-- Timing of the weapon
the T-slot. The T-slot is between the face of the bolt and
is as critical as headspace adjustment. Timing ensures
the rear of the barrel, as shown in figure 13-48. The GO
that firing takes place when the recoiling parts are
end of the gauge should enter the T-slot freely up to the
between .020 and .116 inch out of the battery. That
center ring of the gauge. Remove the gauge and try to
prevents contact between the front end of the barrel
insert the NO-GO end into the T-slot. If the NO-GO end
extension and the trunnion block. Timing is correct
does not enter the slot, headspace distance is correct.
when the following conditions are met:
Headspace Too Tight.-- If the headspace is too tight,
1. The recoiling parts are locked together.
the GO end of the gauge cannot enter the T-slot freely.
To correct this situation, take the following steps:
2. Firing takes place just before the recoiling parts
are in the battery (fully forward).
1. Pull back on the retracting slide handle. Do so
until the lug on the barrel locking spring is visible
3. The gun fires on the FIRE gauge and does not
through the 3/8-inch hole in the right sideplate. (See fig.
fire on the NO-FIRE gauge.
The timing of the gun is checked with the FIRE
2. Unscrew the barrel one notch (click).
(.020 inch) and NO-FIRE (.116 inch) gauges, as shown
in figure 13-49. Timing must be checked and/or set (1)
3. Ease the retracting slide handle and bolt fully
each time headspace is adjusted and (2) whenever the