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 unfired rounds. When the clearing solenoid is 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 Q1. Name the two cycles of the M61A1 gun. Q2. When   does   the   firing   cycle   begin   in   the M61A1 gun? Q3. After  the  projectile  leaves  the  barrel,  what component  removes  the  empty  case  from  the chamber? Q4. The main cam path is _________ shaped. Q5. List,   in   sequence,   the   six   operations   the breech-bolt  assembly  performs  during  a  full firing cycle. Q6. At what point does the clearing cycle start? Q7. 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 systems. 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. 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 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. 6-10