As the breech-bolt assembly picks up a round at the
guide bar, the clearing sector arm depresses the bolt
roller shaft. This locks the bolt assembly in the rear
locking well of the rotor. While locked in this position,
the bolt assembly cannot follow the main cam path, so it
follows the clearing cam path. The clearing cam path
isn't as deep as the main cam path, and it keeps the bolt
roller shaft depressed. This firmly locks the bolt
assembly in the rear of the rotor body.
The M61A1 gun continues to receive rounds during
the clearing cycle. However, because each bolt
assembly remains positioned at the back of the rotor
during rotation, the guide bar cam fingers eject all
deactivated, the clearing sector arm pivots out of the
main cam path. This allows the leaf springs in the rear
locking well to force the bolt-locking block upward.
The bolt roller shaft follows the main cam path that
permits the gun to be fired.
If necessary, you may clear the gun manually. To do
this, manually pivot the clearing sector cam into the
main cam path while turning the rotor by hand.
For further information on the M61A1 automatic
gun, you should refer to the M61A1 Automatic Gun,
NAVAIR 11-95M61A1-1. NAVAIR 11-95M61A1-1
provides intermediate-level maintenance procedures
and includes associated special support equipment.
REVIEW NUMBER 2
Name the two cycles of the M61A1 gun.
When does the firing cycle begin in the
After the projectile leaves the barrel, what
component removes the empty case from the
The main cam path is _________ shaped.
List, in sequence, the six operations the
breech-bolt assembly performs during a full
At what point does the clearing cycle start?
The M61A1 gun continues to receive rounds
during the clearing cycle. What component
ejects all unfired rounds?
AMMUNITION HANDLING AND GUN
ammunition handling and gun drive systems of
the M61A1 automatic gun. Describe the
principles of operation of each system and
identify the interrelationship of the various
The ammunition and gun drive subsystems are
discussed in the following paragraphs.
DRUM UNIT ASSEMBLY
Live ammunition and expended cases are stowed in
the drum unit assembly. This assembly has four major
partsdrum unit, entrance cover, exit cover, and scoop
disk. Refer to figure 6-12 as you read about these parts.
Drum Unit. The drum unit is a cylindrical
structure that consists of an outer drum and an inner
drum helix. The live ammunition rounds and expended
cases are stored radially around the longitudinal axis of
the outer drum with their bases in an outward direction.
Their bases in partitions suspend the rounds. These
partitions are mounted lengthwise with respect to the
inner surface of the outer drum. With the outer drum
mounted stationary to the aircraft's structure, the
rounds are moved along the length of the partitions by
the rotation of the double-lead helix (inner drum). It's
easy to understand this movement if you think of the
inner drum helix as the threads on a screw. The
projectile end of the casing protrudes into the threads.
As the inner drum helix is rotated, it produces a
screwing-type motion, causing the rounds to slide
along the partitions from one end to the other end of the
Entrance Cover. The entrance cover is stationary
mounted to the entrance end of the outer drum. The
entrance cover contains a retainer gear and 252 steel
ball bearings that support the scoop disks and the inner
drum helix. The retainer partitions are mounted to the
retainer gear that controls the position of the rounds as
they are passed from the entrance cover to the scoop
disk. A spring-loaded timing pin on the entrance cover
is used to index the drum for installation of the entrance