the exit unit to the exit cover, press and hold the exit unit
timing pin and the exit cover timing pin to make sure
there is proper gear alignment between the two
components. Once the exit unit is properly attached to
the exit cover, make sure that the spring-loaded timing
The exit unit also contains a last-round switch that
is electrically connected to the gun control firing
circuits. The switch is actuated by the projectiles of the
20-mm rounds. The switch prevents expended rounds
(empty cases) from being fed into the gun and jamming
it, Before the gun will fire, the ammunition must be
cycled through the ammunition drum until the first
round actuates the last-round switch. When there is no
more ammunition present or when expended rounds are
present, the last-round switch is released. This
automatically initiates the gun clearing cycle and
terminates gun firing. Before the gun can be fired again,
live ammunition must be manually positioned by the
ground loading crew to actuate the last-round switch.
The entrance unit is attached over the opening in the
entrance cover and geared to the entrance cover retainer
gear. The entrance unit contains three gear-driven
sprocket assemblies. The sprocket assemblies remove
live rounds or expended cases from the conveyor
elements and place them in the entrance cover retainer
partitions. Before installation, press the spring-loaded
timing pin and align the scoop sprocket stud pin with the
entrance unit timing mark. With the entrance unit
properly timed and aligned, you must press the entrance
cover timing pin and align the timing mark on the scoop
disk with the timing mark on the entrance cover. You
need to properly time and align both the entrance unit
and the entrance cover to ensure proper gear alignment
between the two components. Once the entrance unit is
attached to the entrance cover, you should make sure
that the spring-loaded timing pins release.
TRANSFER UNIT AND ADAPTER
The transfer unit and adapter assembly are actually
two separate components bolted together to form one
unit. They are never separated at the organizational
maintenance level. The function of each component is
discussed in the following paragraphs.
The transfer unit is gear-driven by the gun and
attached to the M61A1 gun housing by quick-release
pins to make maintenance easier. The gear-driven
sprocket assemblies and guides maintain positive
control of the rounds and conveyor elements passing
through the transfer unit. The transfer unit removes the
rounds from the conveyor and places them into the
extractor lip of the gun breech bolts. The transfer unit
also receives expended cases and unfired rounds from
the gun breech bolts and places them in the conveyor
elements. When you install the transfer unit and the
adapter assembly as a single unit, press and hold the
timing pin on the transfer unit and the gun housing.
REVIEW NUMBER 2 ANSWERS TO QUESTIONS Q1. THROUGH Q7.
The two cycles of the M61A1 gun are the firing cycle and the clearing cycle.
The firing cycle begins in the M61A1 gun when power is applied to the firing
after the projectile leaves the barrel, the extractor lip of the breech-bolt assembly
removes the empty case from the chamber.
The main cam path is elliptical shaped.
The six operations the breech-bolt assembly performs during a full firing cycle
are feed, chamber lock and fire, unlock, extract, and eject.
The clearing cycle starts when the clearing solenoid is energized.
The M61A1 gun continues to receive rounds during the clearing cycle. The guide
bar cam fingers eject all unfired rounds.