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 M61A1
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 DRIVE SYSTEMS
LEARNING OBJECTIVE: Identify the
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
parts-drum 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. The
rounds are suspended by their bases in partitions. These
partitions are mounted lengthwise with respect to the
inner surface of the outer drum. With the outer drum
mounted stationary to the aircrafts structure, the rounds
are moved along the length of the partitions by the
rotation of the double-lead helix (inner drum), Its 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 outer drum.
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 unit.
Exit Cover. The exit cover is stationary mounted
to the exit end of the outer drum. The exit cover is
constructed like the entrance cover. It controls the
position of the rounds as they pass from the scoop disk
to the exit cover. A spring-loaded timing pin on the exit
cover is used to index the drum for installation of the
Scoop Disk. A scoop disk is mounted on each end
of the inner drum helix. Each scoop disk has two sets
of sprocket spur gears located 180 degrees apart. These
spur gears mesh with the retainer gear in the
entrance/exit covers that provide rotating support for the
inner drum helix. The sprockets attached to the spur
gear transfer rounds from the entrance cover retainer
partitions to the drum partitions, and from the drum
partitions to the retainer partitions in the exit cover.
The exit unit is attached over an opening in the exit
cover and geared to the exit cover retainer gear. The exit
unit contains two gear-driven sprocket assemblies. The
sprocket assemblies remove live rounds or expended
cases from the retainer partitions in the exit cover and
place them in the conveyor elements. Before you install