Figure 79. Cartridge retainer.
This force (1,130 pounds) is calculated as being applied
to the area in shear. The pressure applied to the total
area of the slot (the pressure necessary to shear the
the cartridge. The retainer also serves a second
case) will be 1,130 pounds per slot or 4,100 psi.
function: it has internal threads at its open end to
Designing the walls of the retainer to withstand this
accommodate the firing pin housing, maintaining firm
internal pressure (assuming that the material between
contact of the housing and cartridge head.
two successive slots is a beam with fixed ends) would
b. Four longitudinal slots, machined in the retainer
result in a wall thickness of 0.120 inch. However, since
wall, permit the cartridge to rupture and the propellant
the rate of loading is extremely high, and the balancing
gas to flow into the chamber. The closed end of the
of pressures as the slots shear, occur so rapidly, the
retainer (the part which supports the base of the
cartridge retainer may be made thinner without danger
cartridge) has four diametral grooves.
When the
of failure. The cartridge retainer has 0.075 inch walls.
initiator is assembled, the end of the retainer is
This thickness was determined by tests.
positioned against the inside face of the exit port end of
the chamber directly over the port, and the grooves form
eight orifices to meter the propellant gas.
Large
initiator is a cylindrical body open at the rear and closed
particles of burning propellant, therefore, are restricted
from escaping from the initiator, hose life is greatly
extended, and gas flow is not blocked.
c. The wall thickness of the retainer must be
chosen to withstand the pressure developed when the
cartridge case is ruptured by the propellant gas. The
case walls are sheared out or partially sheared out
through the slots in the retainer wall when a force, F, is
applied.
F = S3A
S3 = shear stress of 5052 aluminum (18,000
psi)
A = area in shear (periphery of slot X car-
tridge wall thickness)
F = 18,000 X 2.535 X 0.025
F = 1,130 pounds
Figure 80. Initiator chamber.
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