155-MM Howitzer Malfunction Investigation: A Laboratory Study of the Igniter Train Operation
Final rept. Jan-Nov 75
ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD
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On 20 December 1974, two hangfires occurred in a developmental 155-mm howitzer at Aberdeen Proving Ground APG, MD. The second hangfire was accompanied by a rupturing of the howitzer breech. As a result of this, a laboratory study was initiated to uncover possible causes leading to the malfunction. The study involved testing of various components of the igniter train singly and in various combinations under a variety of environmental conditions. The sequence of events leading to the hangfires was as follows the primer ignited the base pad, which did not ignite the propellant nor the black powder containing central core snake. The NC tube ignited to a fizz burn after a period of seconds and eventually ignited the propellant that caused the hangfires. The ignition occurred in a localized region near the breech, leading to the pressure waves of extreme magnitude. Subsequent high pressures that ruptured the breech may have come about because of propellant grain fracture due to pressure wave induced acceleration against the projectile. The difference between the apparently reliable operation of the XM123E2 interim propellant charge and the charge XM203E1 used in the hangfires and in this study was due to the change in igniter train cloths. This was confirmed by post-firing analysis of cloth residues, visual differences in cloth density, and full-scale blowout cannon results.