THE HERO PRIMER


PRIMER DESIGN HISTORY The initial 120 mm family of


FIGURE 1 tank


cartridges qualified with the M125 “thin- walled body” primer in 1984 (Figure 1). Engineers at Picatinny Arsenal, New Jersey, later determined through internal testing that the thin wall could conduct enough heat to the propellant to ignite it in the event that a just-fired primer came in contact with another Abrams tank cartridge. Te first redesign consisted of a rubber coating applied to the M125 thin-walled primer body to prevent heat transfer.


Te next redesign occurred in 1998 with the M125 Electric Primer (Figure 2), which included a thick-wall body, replac- ing the rubber coated thin-walled primer. Te thick wall provides enough ther- mal mass to delay heating of the primer body, preventing premature ignition of the propellant. Tese design changes only affected the body of the primer, not the interior. Te ignition element assembly (IEA) (Figure 3) maintained the same configuration since the 1984 cartridge qualification, and it is the primary charge in the ignition train of the cartridge. Te IEA is what initiates the propellant, expel- ling the cartridge out of the gun tube.


Te manufacture of the legacy M125 electric primer provided its own share of manufacturing issues. Small, fragile parts made automation nearly impossible, and the numerous individual components increased the chances of manufactur- ing defects. Picatinny Arsenal’s Combat Capabilities Development Command (DEVCOM) Armaments Center teams monitored the most critical aspects of the manufacturing process to ensure that a component failure would not risk life or limb. Te quality assurance process inspected for 16 critical defects in the M125 electric primer. A critical defect is a production non-conformance that could


62 Army AL&T Magazine Winter 2022


FIGURE 2


The first 120 mm cartridges qualified with the M125 thin-walled body primer in 1984. (Image courtesy of the author)


FIGURE 3


The addition of a thick-walled body to prevent heat transfer that could cause premature ignition. (Image courtesy of the author)


The ignition element assembly in the M125 electric primer hadn't changed for almost 40 years. (Image courtesy of the author)


The new primer improves manufacturability, decreases susceptibility to electromagnetic safety hazards and reduces manufacturing costs.


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