Figure 77. Delay element.
b. The delay charge is ignited by a percussion
primer. The gas produced during the burning of the
delay charge is contained within the volume of the delay
element. When the delay element burns through (with a
laminar thermal reaction), the igniter is ignited and in
Figure 76. Initiator component layout.
turn ignites the propellant. The length of the delay
element is approximately 1.2 inches.
closed end of the firing pin housing. The initiator
(lanyard) pin withdraws completely providing a
c. The cartridge case selected for the delay
separation between the firing linkage and the initiator.
element and propellant charge had a body diameter of
When the firing pin strikes the cartridge, the primer fires
provided sufficient room for the delay element with its
2 seconds, the delay charge is burned through, igniting
thick walls and allows room for the propellant and igniter
the black powder (igniter) which, in turn, ignites the
propellant. Gas generated by the burning propellant in
d. An M42 percussion primer was selected for use
the cartridge causes the cartridge case to rupture at the
with the cartridge. This primer has an all-fire energy of
unsupported areas, and fills the chamber.
26 inch-ounces. The delay element for this initiator was
propellant gas is metered by the orifices (slots) in the
later standardized as the M5, and the cartridge was
base of the cartridge retainer and is discharged into the
standardized as the M46 delay cartridge.
86. Cartridge. a. Prior to choosing a cartridge case for
the propellant charge, provisions must be made for the
2-second delay. Figure 77 shows the delay element
developed for this initiator. Many standardized delay
elements are available and practice is to use the
standard elements, if applicable, rather than develop
new ones. The delay element consists of four parts: the
retainer, body, primer, and delay charge. The delay
composition consists essentially of barium chromate,
potassium perchlorate, and zirconium nickel alloy.
The delay time is controlled by variations of composition
and weight. The mixture is pressed into pellet form and
inserted, ill increments, into the delay body. A few tests
were made and it was determined that approximately
Figure 78. Initiator cartridge.